Lean 4.19.0 (2025-04-02)🔗

For this release, 414 changes landed. In addition to the 164 feature additions and 74 fixes listed below there were 13 refactoring changes, 29 documentation improvements, 31 performance improvements, 9 improvements to the test suite and 92 other changes.

Language

#5182 makes functions defined by well-founded recursion use an opaque well-founded proof by default. This reliably prevents kernel reduction of such definitions and proofs, which tends to be prohibitively slow (fixes #2171), and which regularly causes hard-to-debug kernel type-checking failures. This changes renders unseal ineffective for such definitions. To avoid the opaque proof, annotate the function definition with @[semireducible].
#5998 lets omega always abstract its own proofs into an auxiliary definition. The size of the olean of Vector.Extract goes down from 20MB to 5MB with this, overall stdlib olean size and build instruction count go down 5%.
#6325 ensures that environments can be loaded, repeatedly, without executing arbitrary code
#7075 ensures that names suggested by tactics like simp? are not shadowed by auxiliary declarations in the local context and that names of let rec and where declarations are correctly resolved in tactic blocks.
#7084 enables the elaboration of theorem bodies, i.e. proofs, to happen in parallel to each other as well as to other elaboration tasks.
#7166 extends the notion of “fixed parameter” of a recursive function also to parameters that come after varying function. The main benefit is that we get nicer induction principles.
#7247 makes generation of match equations and splitters compatible with parallelism.
#7256 introduces the assert! variant debug_assert! that is activated when compiled with buildType debug.
#7261 ensures all equation, unfold, induction, and partial fixpoint theorem generators in core are compatible with parallelism.
#7298 adds rewrites to bv_decide's preprocessing that concern combinations of if-then-else and operation such as multiplication or negation.
#7302 changes how fields are elaborated in the structure/class commands and also makes default values respect the structure resolution order when there is diamond inheritance. Before, the details of subobjects were exposed during elaboration, and in the local context any fields that came from a subobject were defined to be projections of the subobject field. Now, every field is represented as a local variable. All parents (not just subobject parents) are now represented in the local context, and they are now local variables defined to be parent constructors applied to field variables (inverting the previous relationship). Other notes:
- The entire collection of parents is processed, and all parent projection names are checked for consistency. Every parent appears in the local context now.
- For classes, every parent now contributes an instance, not just the parents represented as subobjects.
- Default values are now processed according to the parent resolution order. Default value definition/override auxiliary definitions are stored at StructName.fieldName._default, and inherited values are stored at StructName.fieldName._inherited_default. Metaprograms no longer need to look at parents when doing calculations on default values.
- Default value omission for structure instance notation pretty printing has been updated in consideration of this.
- Now the elaborator generates a _flat_ctor constructor that will be used for structure instance elaboration. All types in this constructor are put in "field normal form" (projections of parent constructors are reduced, and parent constructors are eta reduced), and all fields with autoParams are annotated as such. This is not meant for users, but it may be useful for metaprogramming.
- While elaborating fields, any metavariables whose type is one of the parents is assigned to that parent. The hypothesis is that, for the purpose of elaborating structure fields, parents are fixed: there is only one instance of any given parent under consideration. See the Magma test for an example of this being necessary. The hypothesis may not be true when there are recursive structures, since different values of the structure might not agree on parent fields.
#7304 fixes an issue where nested let rec declarations within match expressions or tactic blocks failed to compile if they were nested within, and recursively called, a let rec that referenced a variable bound by a containing declaration.
#7309 fixes a bug where bv_decide's new structure support would sometimes not case split on all available structure fvars as their type was an mvar.
#7312 implements proof term generation for cooper_dvd_left and its variants in the cutsat procedure for linear integer arithmetic.
#7314 changes elaboration of structure parents so that each must be fully elaborated before the next one is processed.
#7315 implements the Cooper conflict resolution in cutsat. We still need to implement the backtracking and disequality case.
#7324 changes the internal construction of well-founded recursion, to not change the type of fix’s induction hypothesis in non-defeq ways.
#7329 adds support to bv_decide for simple pattern matching on enum inductives. By simple we mean non dependent match statements with all arms written out.
#7333 allows aux decls (like generated by match) to be generated by decreasing_by tactics.
#7335 modifies elabTerminationByHints in a way that the type of the recursive function used for elaboration of the termination measure is striped of from optional parameters. It prevents introducing dependencies between the default values for arguments, that can cause the termination checker to fail.
#7339 implements cooper conflict resolution in the cutsat procedure. It also fixes several bugs in the proof term construction. We still need to add more tests, but we can already solve the following example that omega fails to solve:
```
example (x y : Int) :
    27 ≤ 11*x + 13*y →
    11*x + 13*y ≤ 45 →
    -10 ≤ 7*x - 9*y →
    7*x - 9*y ≤ 4 → False := by
  grind
```
#7347 upgrades the CaDiCal we ship and use for bv_decide to version 2.1.2. Additionally it enables binary LRAT proofs on windows by default as https://github.com/arminbiere/cadical/issues/112 has been fixed.
#7348 ensures all equation and unfold theorem generators in core are compatible with parallelism.
#7351 ensures cutsat does not have to perform case analysis in the univariate polynomial case. That it, it can close a goal whenever there is no solution for a divisibility constraint in an interval. Example of theorem that is now proved in a single step by cutsat:
```
example (x : Int) : 100 ≤ x → x ≤ 10000 → 20000 ∣ 3*x → False := by
  grind
```
#7353 changes abstractNestedProofs so that it also visits the subterms in the head of an application.
#7355 fixes a bug in the markNestedProofs preprocessor used in the grind tactic.
#7357 adds support for / and % to the cutsat procedure.
#7362 allows simp dischargers to add aux decls to the environment. This enables tactics like native_decide to be used here, and unblocks improvements to omega in #5998.
#7369 uses let-declarations for each polynomial occurring in a proof term generated by the cutsat procedure.
#7370 simplifies the proof term due to the Cooper's conflict resolution in cutsat.
#7373 implements the last missing case for the cutsat procedure and fixes a bug. During model construction, we may encounter a bounded interval containing integer solutions that satisfy the divisibility constraint but fail to satisfy known disequalities.
#7381 refactors the AIG datastructures that underly bv_decide in order to allow a better tracking of negations in the circuit. This refactor has two effects, for one adding full constant folding to the AIG framework and secondly enabling us to add further simplifications from the Brummayer Biere paper in the future which was previously architecturally impossible.
#7387 uses -implicitDefEqProofs in bv_omega to ensure it is not affected by the change in #7386.
#7390 makes bv_decide's preprocessing handle casts, as we are in the constant BitVec fragment we should be able to always remove them using BitVec.cast_eq.
#7392 fixes an issue in the grind tactic when case splitting on if-then-else expressions.
#7394 adds infrastructure necessary for supporting Nat in the cutsat procedure. It also makes the grind more robust.
#7396 fixes a bug in the cutsat model construction. It was searching for a solution in the wrong direction.
#7397 ensures that Poly.mul p 0 always returns Poly.num 0.
#7401 improves the cutsat model search procedure by tightening inequalities using divisibility constraints.
#7407 adds rules for -1#w * a = -a and a * -1#w = -a to bv_normalize as seen in Bitwuzla's BV_MUL_SPECIAL_CONST.
#7409 allows the use of dsimp during preprocessing of well-founded definitions. This fixes regressions when using if-then-else without giving a name to the condition, but where the condition is needed for the termination proof, in cases where that subexpression is reachable only by dsimp, but not by simp (e.g. inside a dependent let)
#7417 adds support for enum inductive matches with default branches to bv_decide.
#7429 adds the BV_EXTRACT_FULL preprocessing rule from Bitwuzla to bv_decide.
#7431 changes the syntax of location modifiers for tactics like simp and rw (e.g., simp at h ⊢) to allow the turnstile ⊢ to appear anywhere in the sequence of locations.
#7436 adds simprocs that turn left and right shifts by constants into extracts to bv_decide.
#7438 adds the EQUAL_CONST_BV_ADD and BV_AND_CONST rules to bv_decide's preprocessor.
#7441 adds the BV_CONCAT_CONST, BV_CONCAT_EXTRACT and ELIM_ZERO_EXTEND rule from Bitwuzla to bv_decide.
#7457 ensures info tree users such as linters and request handlers have access to info subtrees created by async elab task by introducing API to leave holes filled by such tasks.
#7477 ensures that bv_decide doesn't accidentally operate on terms underneath binders. As there is currently no binder construct that is in the supported fragment of bv_decide this changes nothing about the proof power.
#7480 adds the necessary rewrites for the Bitwuzla rules BV_ULT_SPECIAL_CONST, BV_SIGN_EXTEND_ELIM, TODO.
#7486 adds the BitVec.add_neg_mul rule introduced in #7481 to bv_decide's preprocessor.
#7491 achieves a speed up in bv_decide's LRAT checker by improving its input validation.
#7494 implements support for Nat inequalities in the cutsat procedure.
#7495 implements support for Nat divisibility constraints in the cutsat procedure.
#7501 implements support for Nat equalities and disequalities in the cutsat procedure.
#7502 implements support for Nat div and mod in the cutsat procedure.
#7503 implements support for Nat.sub in cutsat
#7509 disables the implicitDefEqProofs simp option in the preprocessor of bv_decide in order to account for regressions caused by #7387.
#7510 ensures that grind can be used as a more powerful contradiction tactic, sparing the user from having to type exfalso; grind or intros; exfalso; grind.
#7511 fixes two bugs in simp +arith that were preventing specific subterms from being normalized.
#7512 adds missing normalization rules for Nat div and mod to the grind tactic.
#7514 adds more missing normalization rules for div and mod to grind.
#7515 fixes another bug in simp +arith. This bug was affecting grind. See new test for an example.
#7521 adds the equivalent of Array.emptyWithCapacity to the AIG framework and applies it to bv_decide. This is particularly useful as we are only working with capacities that are always known at run time so we should never have to reallocate a RefVec.
#7527 adds the BV_EXTRACT_CONCAT_LHS_RHS, NORM_BV_ADD_MUL and NORM_BV_SHL_NEG rewrite from Bitwuzla as well as a reduction from getLsbD to extractLsb' to bv_decide.
#7532 fixes the procedure for putting new facts into the grind "to-do" list. It ensures the new facts are preprocessed. also removes some of the clutter in the Nat.sub support.
#7536 implements support for ¬ d ∣ p in the cutsat procedure.
#7537 implements support for Int.natAbs and Int.toNat in the cutsat procedure.
#7538 fixes a bug in the cutsat model construction. It was not resetting the decision stack at the end of the search.
#7540 adds [grind cases eager] attribute to Subtype. See new test.
#7551 changes isNatCmp to ignore optional arguments annotations, when checking for <-like comparison between elements of Nat. That previously caused guessLex to fail when checking termination of a function, whose signature involved an optional argument of the type Nat.
#7553 removes a bad normalization rule in grind, and adds a missing dsimproc.
#7560 ensures that we use the same ordering to normalize linear Int terms and relations. This change affects simp +arith and grind normalizer.
#7561 fixes the support for nonlinear Nat terms in cutsat. For example, cutsat was failing in the following example
```
example (i j k l : Nat) : i / j + k + l - k = i / j + l := by grind
```
because we were not adding the fact that i / j is non negative when we inject the Nat expression into Int.
#7579 improves the counterexamples produced by the cutsat procedure, and adds proper support for Nat. Before this PR, the assignment for an natural variable x would be represented as NatCast.natCast x.
#7615 adds the ADD part of bitwuzlas BV_EXTRACT_ADD_MUL rule to bv_decide's preprocessor.
#7617 adds the known bits optimization from the multiplication circuit to the add one, allowing us to discover potentially even more symmetries before going to the SAT solver.
#7622 fixes fun_induction when used on structurally recursive functions where there are targets occurring before fixed parameters.
#7630 fixes a performance issue in the whnfCore procedure.
#7636 makes sure that the expression level cache in bv_decide is maintained across the entire bitblaster instead of just locally per BitVec expression.
#7640 implements the main logic for inheriting and overriding autoParam fields in the structure/class commands, pending being enabled in the structure instance notation elaborator. Adds term info to overridden fields, so they now can be hovered over, and "go to definition" goes to the structure the field is originally defined in.

#7641 implements basic model-based theory combination in grind. grind can now solve examples such as

example (f : Int → Int) (x : Int)
    : 0 ≤ x → x ≠ 0 → x ≤ 1 → f x = 2 → f 1 = 2 := by
  grind

#7644 adds a cache to the reflection procedure of bv_decide.
#7649 changes the AIG representation of constants from const (b : Bool) to a single constructor false. Since #7381 Ref contains an invert flag meaning the constant true can be represented as a Ref to false with invert set, so no expressivity is lost.
#7652 gives #print for structures the ability to show the default values and auto-param tactics for fields.
#7655 adds the preprocessing rule for extraction over multiplication to bv_decide.
#7663 uses computed fields to store the hash code and pointer equality to increase performance of comparison and hashmap lookups on the core data structure used by the bitblaster.
#7670 improves the caching computation of the atoms assignment in bv_decide's reflection procedure.
#7698 adds more sharing and caching procedures to bv_decide's reflection step.
#7712 ensures grind always abstract its own proofs into an auxiliary definition/theorem. This is similar to #5998 but for grind
#7714 fixes an assertion violation in the grind model-based theory combination module.
#7717 changes how {...}/where notation ("structure instance notation") elaborates. The notation now tries to simulate a flat representation as much as possible, without exposing the details of subobjects. Features:
- When fields are elaborated, their expected types now have a couple reductions applied. For all projections and constructors associated to the structure and its parents, projections of constructors are reduced and constructors of projections are eta reduced, and also implementation detail local variables are zeta reduced in propositions (so tactic proofs should never see them anymore). Furthermore, field values are beta reduced automatically in successive field types. The example in mathlib4#12129 now shows a goal of 0 = 0 rather than { toFun := fun x => x }.toFun 0 = 0.
- All parents can now be used as field names, not just the subobject parents. These are like additional sources but with three constraints: every field of the value must be used, the fields must not overlap with other provided fields, and every field of the specified parent must be provided for. Similar to sources, the values are hoisted to lets if they are not already variables, to avoid multiple evaluation. They are implementation detail local variables, so they get unfolded for successive fields.
- All class parents are now used to fill in missing fields, not just the subobject parents. Closes #6046. Rules: (1) only those parents whose fields are a subset of the remaining fields are considered, (2) parents are considered only before any fields are elaborated, and (3) only those parents whose type can be computed are considered (this can happen if a parent depends on another parent, which is possible since #7302).
- Default values and autoparams now respect the resolution order completely: each field has at most one default value definition that can provide for it. The algorithm that tries to unstick default values by walking up the subobject hierarchy has been removed. If there are applications of default value priorities, we might consider it in a future release.
- The resulting constructors are now fully packed. This is implemented by doing structure eta reduction of the elaborated expressions.
- "Magic field definitions" (as reported on Zulip) have been eliminated. This was where fields were being solved for by unification, tricking the default value system into thinking they had actually been provided. Now the default value system keeps track of which fields it has actually solved for, and which fields the user did not provide. Explicit structure fields (the default kind) without any explicit value definition will result in an error. If it was solved for by unification, the error message will include the inferred value, like "field 'f' must be explicitly provided, its synthesized value is v"
- When the notation is used in patterns, it now no longer inserts fields using class parents, and it no longer applies autoparams or default values. The motivation is that one expects patterns to match only the given fields. This is still imperfect, since fields might be solved for indirectly.
- Elaboration now attempts error recovery. Extraneous fields log errors and are ignored, missing fields are filled with sorry.
#7720 compresses the AIG representation by storing the inverter bit in the lowest bit of the gate descriptor instead of as a separate Bool.
#7723 adds the configuration options zeta and zetaDelta in grind. Both are set to true by default.
#7724 adds dite_eq_ite normalization rule to grind. This rule is important to adjust mismatches between a definition and its function induction principle.
#7726 fixes the markNestedProofs procedure used in grind. It was missing the case where the type of a nested proof may contain other nested proofs.
#7727 avoids some unnecessary allocations in the CNF to dimacs conversion
#7728 fixes an issue in abstractNestedProofs. We should abstract proofs occurring in the inferred proposition too.
#7733 ensures that in the AIG the constant circuit node is always stored at the first spot. This allows us to skip performing a cache lookup when we require a constant node.
#7742 adds a feature to structure/class where binders without types on a field definition are interpreted as overriding the type's parameters binder kinds in that field's projection function. The rules are (1) only a prefix of the binders are interpreted this way, (2) multi-identifier binders are allowed but they must all be for parameters, (3) only parameters that appear in the declaration itself (not from variables) can be overridden and (4) the updates will be applied after parameter binder kind inference is done. Binder updates are not allowed in default value redefinitions. Example application: In the following, (R p) causes the R and p parameters to be explicit, where normally they would be implicit.
```
class CharP (R : Type u) [AddMonoidWithOne R] (p : Nat) : Prop where
  cast_eq_zero_iff (R p) : ∀ x : Nat, (x : R) = 0 ↔ p ∣ x
```
#7746 adds declaration ranges to structure fields that were copied from parents that aren't represented as subobjects, supporting "go to definition". The declaration range is the parent in the extends clause.
#7760 ensures grind is using the default transparency setting when computing auxiliary congruence lemmas.
#7765 improves how grind normalizes dependent implications during introduction. Previously, grind would introduce a hypothesis h : p for a goal of the form .. ⊢ (h : p) → q h, and then normalize and assert a non-dependent copy of p. As a result, the local context would contain both h : p and a separate h' : p', where p' is the normal form of p. Moreover, q would still depend on the original h.
#7776 improves the equality proof discharger used by the E-matching procedure in grind.
#7777 fixes the introduction procedure used in grind. It was not registering local instances that are also propositions. See new test.
#7778 adds missing propagation rules for LawfulBEq A to grind. They are needed in a context where the instance DecidableEq A is not available. See new test.
#7781 adds a new propagation rule for Bool disequalities to grind. It now propagates x = true (x = false) from the disequality x = false (x = true). It ensures we don't have to perform case analysis on x to learn this fact. See tests.

Library

#6496 adds short-circuit support to bv_decide to accelerate multiplications with shared coefficients. In particular, a * x = b * x can be extended to a = b v (a * x = b * x). The latter is faster if a = b is true, as a = b may be evaluated without considering the multiplication circuit. On the other hand, we require the multiplication circuit, as a * x = b * x -> a = b is not always true due to two's complement wrapping.
#6683 introduces TCP socket support using the LibUV library, enabling asynchronous I/O operations with it.
#7104 adds BitVec.[toNat|toFin|toInt]_[sshiftRight|sshiftRight'] plus variants with of_msb_*. While at it, we also add toInt_zero_length and toInt_of_zero_length. In support of our main theorem we add toInt_shiftRight_lt and le_toInt_shiftRight, which make the main theorem automatically derivable via omega.
#7141 generalizes cond to allow the motive to be in Sort u, not just Type u.
#7225 contains BitVec.(toInt, toFin)_twoPow theorems, completing the API for BitVec.*_twoPow. It also expands the toNat_twoPow API with toNat_twoPow_of_le, toNat_twoPow_of_lt, as well as toNat_twoPow_eq_if and moves msb_twoPow up, as it is used in the toInt_msb proof.
#7228 adds simprocs to reduce expressions involving IntX.
#7270 provides lemmas about the tree map functions foldlM, foldl, foldrM and foldr and their interactions with other functions for which lemmas already exist. Additionally, it generalizes the fold*/keys lemmas to arbitrary tree maps, which were previously stated only for the DTreeMap α Unit case.
#7274 adds lemmas about iterated conversions between finite types, starting with something of type IntX.
#7289 adds getKey_beq, getKey_congr and variants to the hashmap api.
#7319 continues alignment of lemmas about Int.ediv/fdiv/tdiv, including adding notes about "missing" lemmas that do not apply in one case. Also lemmas about emod/fmod/tmod. There's still more to do.
#7331 provides lemmas about the tree map function insertMany and its interaction with other functions for which lemmas already exist. Most lemmas about ofList, which is related to insertMany, are not included.
#7338 adds @[simp] to Int.neg_inj.
#7340 adds lemmas for iterated conversions between finite types which start with Nat/Int/Fin/BitVec and then go through UIntX.
#7341 adds an equivalence relation to the hash map with several lemmas for it.
#7356 adds lemmas reducing monadic operations with pure to the non-monadic counterparts.
#7358 fills further gaps in the integer division API, and mostly achieves parity between the three variants of integer division. There are still some inequality lemmas about tdiv and fdiv that are missing, but as they would have quite awkward statements I'm hoping that for now no one is going to miss them.
#7360 provides lemmas about the tree map function ofList and interactions with other functions for which lemmas already exist.
#7367 provides lemmas for the tree map functions alter and modify and their interactions with other functions for which lemmas already exist.
#7368 adds lemmas for iterated conversions between finite types, starting with something of type Nat/Int/Fin/BitVec and going through IntX.
#7378 adds lemmas about Int that will be required in #7368.
#7380 moves DHashMap.Raw.foldRev(M) into DHashMap.Raw.Internal.
#7406 makes the instance for Subsingleton (Squash α) work for α : Sort u.
#7412 provides lemmas about the tree map that have been introduced to the hash map in #7289.
#7414 adds the remaining lemmas about iterated conversions of finite type that go through signed or unsigned bounded integers.
#7415 adds a few lemmas about the interactions of BitVec with Fin and Nat.
#7418 renames several hash map lemmas (get -> getElem) and uses m[k]? instead of get? m k (and also for get! and get).
#7419 provides lemmas about the tree map function modify and its interactions with other functions for which lemmas already exist.
#7420 generalizes BitVec.toInt_[lt|le]' to not require 0 < w.

#7424 proves Bitwuzla's rule BV_ZERO_EXTEND_ELIM:

theorem setWidth_eq_append {v : Nat} {x : BitVec v} {w : Nat} (h : v ≤ w) :
    x.setWidth w = ((0#(w - v)) ++ x).cast (by omega) := by

#7426 adds the Bitwuzla rewrite rule BV_EXTRACT_FULL, which is useful for the bitblaster to simplify extractLsb' based expressions.
#7427 implements the bitwuzla rule BV_CONCAT_EXTRACT. This will be used by the bitblaster to simplify adjacent extracts into a single extract.
#7432 adds a consequence of Nat.add_div using a divisibility hypothesis.
#7433 makes simp able to simplify basic for loops in monads other than Id.
#7435 reviews the Nat and Int API, making the interfaces more consistent.
#7437 provides (some but not all) lemmas about the tree map function minKey?.
#7445 renames Array.mkEmpty to emptyWithCapacity. (Similarly for ByteArray and FloatArray.)
#7446 prefers using ∅ instead of .empty functions. We may later rename .empty functions to avoid the naming clash with EmptyCollection, and to better express semantics of functions which take an optional capacity argument.
#7451 renames the member insert_emptyc_eq of the LawfulSingleton typeclass to insert_empty_eq to conform to the recommended spelling of ∅ as empty.
#7454 implements the bitwuzla rule BV_SIGN_EXTEND_ELIM, which rewrites a signExtend x as an append of the appropriate sign bits, followed by the bits of x.
#7461 introduces a bitvector associativity/commutativity normalization on bitvector terms of the form (a * b) = (c * d) for a, b, c, d bitvectors. This mirrors Bitwuzla's PassNormalize::process's PassNormalize::normalize_eq_add_mul.

#7465 adds the theorem:

theorem lt_allOnes_iff {x : BitVec w} : x < allOnes w ↔ x ≠ allOnes w

to simplify comparisons against -1#w. This is a corollary of the existing lemma:

theorem allOnes_le_iff {x : BitVec w} : allOnes w ≤ x ↔ x = allOnes w

#7466 further cleans up simp lemmas for Int.
#7481 implements the Bitwuzla rewrites BV_ADD_NEG_MUL, and associated lemmas to make the proof streamlined. bvneg (bvadd a (bvmul a b)) = (bvmul a (bvnot b)), or spelled as lean:
```
theorem neg_add_mul_eq_mul_not {x y : BitVec w} :
    - (x + x * y) = (x * ~~~ y)
```

#7482 implements the BV_EXTRACT_CONCAT rule from Bitwuzla, which explains how to extract bits from an append. We first prove a 'master theorem' which has the full case analysis, from which we rapidly derive the necessary BV_EXTRACT_CONCAT theorems:

theorem extractLsb'_append_eq_ite {v w} {xhi : BitVec v} {xlo : BitVec w} {start len : Nat} :
    extractLsb' start len (xhi ++ xlo) =
    if hstart : start < w
    then
      if hlen : start + len < w
      then extractLsb' start len xlo
      else
        (((extractLsb' (start - w) (len - (w - start)) xhi) ++
            extractLsb' start (w - start) xlo)).cast (by omega)
    else
      extractLsb' (start - w) len xhi

#7484 adds some lemmas about operations defined on UIntX
#7487 adds the instance Neg UInt8.
#7493 implements the Bitwuzla rewrite rule NORM_BV_ADD_MUL, and the associated lemmas to allow for expedient rewriting:
```
theorem neg_add_mul_eq_mul_not {x y : BitVec w} : - (x + x * y) = x * ~~~ y
```
#7508 shows that negation commutes with left shift, which is the Bitwuzla rewrite NORM_BV_SHL_NEG.
#7516 changes the order of arguments for List.modify and List.insertIdx, making them consistent with Array.
#7522 splits off the required theory about Nat, Fin and BitVec from #7484.
#7529 upstreams bind_congr from Mathlib and proves that the minimum of a sorted list is its head and weakens the antisymmetry condition of min?_eq_some_iff. Instead of requiring an Std.Antisymm instance, min?_eq_some_iff now only expects a proof that the relation is antisymmetric on the elements of the list. If the new premise is left out, an autoparam will try to derive it from Std.Antisymm, so existing usages of the theorem will most likely continue to work.
#7541 corrects names of a number of lemmas, where the incorrect name was identified automatically by a tool written by @Rob23oba.
#7554 adds SMT-LIB operators to detect overflow BitVec.negOverflow, according to the SMTLIB standard, and the theorem proving equivalence of such definition with the BitVec library functions (negOverflow_eq).
#7556 provides lemmas about the tree map function minKey? and its interaction with other functions for which lemmas already exist.
#7558 changes the definition of Nat.div and Nat.mod to use a structurally recursive, fuel-based implementation rather than well-founded recursion. This leads to more predicable reduction behavior in the kernel.
#7565 adds BitVec.toInt_sdiv plus a lot of related bitvector theory around divisions.
#7571 fixes #7478 by modifying number specifiers from atLeast size to flexible size for parsing. This change allows:
- 1 repetition to accept 1 or more characters
- More than 1 repetition to require exactly that many characters
#7574 introduces UDP socket support using the LibUV library, enabling asynchronous I/O operations with it.
#7578 introduces a function called interfaceAddresses that retrieves an array of system’s network interfaces.
#7584 introduces a structure called FormatConfig, which provides additional configuration options for GenericFormat, such as whether leap seconds should be allowed during parsing. By default, this option is set to false.
#7592 adds theory about signed finite integers relating operations and conversion functions.
#7594 implements the Bitwuzla rewrites BV_EXTRACT_ADD_MUL, which witness that the high bits at i >= len do not affect the bits of the product upto len.
#7595 implements the addition rewrite from the Bitwuzla rewrite BV_EXTRACT_ADD_MUL, which witness that the high bits at i >= len do not affect the bits of the sum upto len:
```
theorem extractLsb'_add {w len} {x y : BitVec w} (hlen : len ≤ w) :
    (x + y).extractLsb' 0 len = x.extractLsb' 0 len + y.extractLsb' 0 len
```
#7598 adds miscellaneous results about Nat and BitVec that will be required for IntX theory (#7592).
#7599 adds SMT-LIB operators to detect overflow BitVec.(usubOverflow, ssubOverflow), according to the SMTLIB standard, and the theorems proving equivalence of such definition with the BitVec library functions BittVec.(usubOverflow_eq, ssubOverflow_eq).
#7600 provides lemmas about the tree map function minKey! and its interactions with other functions for which lemmas already exist.
#7604 adds bitvector theorems that to push negation into other operations, following Hacker's Delight: Ch2.1.
#7605 adds theorems BitVec.[(toInt, toFin)_(extractLsb, extractLsb')], completing the API for BitVec.(extractLsb, extractLsb').
#7614 marks Nat.div and Nat.modCore as irreducible, to recover the behavior from from before #7558.
#7616 introduces BitVec.(toInt, toFin)_rotate(Left, Right), completing the API for BitVec.rotate(Left, Right)
#7626 provides lemmas for the tree map function minKeyD and its interations with other functions for which lemmas already exist.
#7657 provides lemmas for the tree map function maxKey? and its interations with other functions for which lemmas already exist.
#7658 introduces BitVec.(toFin_signExtend_of_le, toFin_signExtend), completing the API for BitVec.signExtend.
#7660 provides lemmas for the tree map function minKey and its interations with other functions for which lemmas already exist.
#7661 adds theorems BitVec.[(toFin, toInt)_setWidth', msb_setWidth'_of_lt, toNat_lt_twoPow_of_le, toInt_setWidth'_of_lt], completing the API for BitVec.setWidth'.
#7664 fixes a bug in the definition of the tree map functions maxKey and maxEntry. Moreover, it provides lemmas for this function and its interactions with other function for which lemmas already exist.
#7672 reviews the implicitness of arguments across List/Array/Vector, generally trying to make arguments implicit where possible, although sometimes correcting propositional arguments which were incorrectly implicit to explicit.
#7674 add missing lemmas about the tree map: minKey* variants return the head of keys, keys and toList are ordered and getKey* t.minKey? equals the minimum.
#7675 provides lemmas about the tree map function maxKeyD and its interactions with other functions for which lemmas already exist.
#7685 contains additional material about BitVec and Int spun off from #7592.
#7686 provides lemmas for the tree map function maxKey! and its interactions with other functions for which lemmas already exist.
#7687 provides Inhabited, Ord (if missing), TransOrd, LawfulEqOrd and LawfulBEqOrd instances for various types, namely Bool, String, Nat, Int, UIntX, Option, Prod and date/time types. It also adds a few related theorems, especially about how the Ord instance for Int relates to LE and LT.
#7692 upstreams a small number of ordering lemmas for Fin from mathlib.
#7694 contains additional material on BitVec, Int and Nat, split off from #7592.
#7695 removes simp lemmas about the tree map with a metavariable in the head of the discrimination pattern.
#7697 is a follow-up to #7695, which removed simp attributes from tree map lemmas with bad discrimination patterns. In this PR, we introduce some Ord-based lemmas that are more simp-friendly.
#7699 adds the BitVec.toInt_srem lemma, relating BitVec.srem with Int.tmod.
#7700 provides Ord-related instances such as TransOrd for IntX, Ordering, BitVec, Array, List and Vector.
#7704 adds lemmas about the modulo operation defined on signed bounded integers.
#7706 performs various cleanup tasks on Init/Data/UInt/* and Init/Data/SInt/*.
#7729 replaces assert! with assertBEq to fix issues where asserts didn't trigger the ctest due to being in a separate task. This was caused by panics not being caught in tasks, while IO errors were handled by the AsyncTask if we use the block function on them.
#7751 adds Std.BaseMutex.tryLock and Std.Mutex.tryAtomically as well as unit tests for our locking and condition variable primitives.
#7755 adds Std.RecursiveMutex as a recursive/reentrant equivalent to Std.Mutex.
#7756 adds lemmas about Nat.gcd (some of which are currently present in mathlib).
#7757 adds the Bitwuzla rewrite NORM_BV_ADD_CONCAT for symbolic simplification of add-of-append.
#7771 adds a barrier primitive as Std.Barrier.

Compiler

#7398 fixes a scoping error in the cce (Common Case Elimination) pass of the old code generator. This pass would create a join point for common minor premises even if some of those premises were in the bodies of locally defined functions, which results in an improperly scoped reference to a join point. The fix is to save/restore candidates when visiting a lambda.
#7710 improves memory use of Lean, especially for longer-running server processes, by up to 60%

Pretty Printing

#7589 changes the structure instance notation pretty printer so that fields are omitted if their value is definitionally equal to the default value for the field (up to reducible transparancy). Setting pp.structureInstances.defaults to true forces such fields to be pretty printed anyway.

Documentation

#7198 makes the docstrings in the Char namespace follow the documentation conventions.
#7204 adds docstrings for the Id monad.
#7246 updates existing docstrings for Bool and adds the missing ones.
#7288 fixes the doc of List.removeAll
#7365 updates docstrings and adds some that are missing.
#7452 makes the style of all List docstrings that appear in the language reference consistent.
#7476 adds missing docstrings for IO and related code and makes the style of the existing docstrings consistent.
#7492 adds missing Array docstrings and makes their style consistent.
#7506 adds missing String docstrings and makes the existing ones consistent in style.
#7523 adds missing docstrings and makes docstring style consistent for System and System.FilePath.
#7528 makes the docstrings for Thunk consistent with the style of the others.
#7534 adds missing Syntax-related docstrings and makes the existing ones consistent in style with the others.
#7535 revises the docstring for funext, making it more concise and adding a reference to the manual for more details.
#7548 adds missing monad transformer docstrings and makes their style consistent.
#7552 adds missing Nat docstrings and makes their style consistent.
#7564 updates the docstrings for ULift and PLift, making their style consistent with the others.
#7568 adds missing Int docstrings and makes the style of all of them consistent.
#7602 adds missing docstrings for fixed-width integer operations and makes their style consistent.
#7607 adds docstrings for String.drop and String.dropRight.
#7613 adds a variety of docstrings for names that appear in the manual.
#7635 adds missing docstrings for Substring and makes the style of Substring docstrings consistent.
#7642 reviews the docstrings for Float and Float32, adding missing ones and making their format consistent.
#7645 adds missing docstrings and makes docstring style consistent for ForM, ForIn, ForIn', ForInStep, IntCast, and NatCast.
#7711 adds the last few missing docstrings that appear in the manual.
#7713 makes the BitVec docstrings match each other and the rest of the API in style.

Server

#7178 fixes a race condition in the language server that would sometimes cause it to drop requests and never respond to them when editing the header of a file. This in turn could cause semantic highlighting to stop functioning in VS Code, as VS Code would stop emitting requests when a prior request was dropped, and also cause the InfoView to become defective. It would also cause import auto-completion to feel a bit wonky, since these requests were sometimes dropped. This race condition has been present in the language server since its first version in 2020.
#7223 implements parallel watchdog request processing so that requests that are processed by the watchdog cannot block the main thread of the watchdog anymore.
#7240 adds a canonical syntax for linking to sections in the language reference along with formatting of examples in docstrings according to the docstring style guide.
#7343 mitigates an issue where inserting an inlay hint in VS Code by double-clicking would insert the inlay hint at the wrong position right after an edit.
#7344 combines the auto-implicit inlay hint tooltips into a single tooltip. This works around an issue in VS Code where VS Code fails to update hovers for tooltips in adjacent inlay hint parts when moving the mouse.
#7346 fixes an issue where the language server would run into an inlay hint assertion violation when deleting a file that is still open in the language server.
#7366 adds server-side support for dedicated 'unsolved goals' and 'goals accomplished' diagnostics that will have special support in the Lean 4 VS Code extension. The special 'unsolved goals' diagnostic is adapted from the 'unsolved goals' error diagnostic, while the 'goals accomplished' diagnostic is issued when a theorem or Prop-typed example has no errors or sorrys. The Lean 4 VS Code extension companion PR is at leanprover/vscode-lean4#585.
#7376 ensures weak options do not have to be repeated in both Lake leanOptions and moreServerOptions.

Lake

#7185 refactors Lake's build internals to enable the introduction of targets and facets beyond packages, modules, and libraries. Facets, build keys, build info, and CLI commands have been generalized to arbitrary target types.
#7393 adds autocompletion support for Lake configuration fields in the Lean DSL at the indented whitespace after an existing field. Autocompletion in the absence of any fields is currently still not supported.
#7399 reverts the new builtin initializers, elaborators, and macros in Lake back to non-builtin.
#7504 augments the Lake configuration data structures declarations (e.g., PackageConfig, LeanLibConfig) to produce additional metadata which is used to automatically generate the Lean & TOML encoders and decoders via metaprograms.
#7543 unifies the configuration declarations of dynamic targets, external libraries, Lean libraries, and Lean executables into a single data type stored in a unified map within a package.
#7576 changes Lake to produce and use response files on Windows when building executables and libraries (static and shared). This is done to avoid potentially exceeding Windows command line length limits.
#7586 changes the static.export facet for Lean libraries to produce thin static libraries.
#7608 removes the use of the Lake plugin in the Lake build and in configuration files.
#7667 changes Lake to log messages from a Lean configuration the same way it logs message from a Lean build. This, for instance, removes redundant severity captions.
#7703 adds input_file and input_dir as new target types. It also adds the needs configuration option for Lean libraries and executables. This option generalizes extraDepTargets (which will be deprecated in the future), providing much richer support for declaring dependencies across package and target type boundaries.
#7716 adds the moreLinkObjs and moreLinkLibs options for Lean packages, libraries, and executables. These serves as functional replacements for extern_lib and provided additional flexibility.
#7732 deprecates extraDepTargets and fixes a bug caused by the configuration refactor.
#7758 removes the -lstdcpp extra link argument from the FFI example. It is not actually necessary.
#7763 corrects build key fetches to produce jobs with the proper data kinds and fixes a failed coercion from key literals to targets.

Other

#7326 updates the release notes script to better indent PR descriptions.
#7453 adds "(kernel)" to the message for the kernel-level application type mismatch error.
#7769 fixes a number of bugs in the release automation scripts, adds a script to merge tags into remote stable branches, and makes the main release_checklist.py script give suggestions to call the merge_remote.py and release_steps.py scripts when needed.