…set_insert` (#28285)

I see some other similar theorems such as `List.cons_sublist_cons` and `Finset.cons_subset_cons` are already marked with `@[simp]` annotations. Doing this enables the following statements to be proved simpler with a single `simp`, which in turn makes proofs more easily found by proof search tactics:

```lean
example a b c : {a, b} ≤ ({a, b, c} : Multiset ℝ) := by
  simp

example a b : {a, b} ≤ ({a, a, b, b} : Multiset ℝ) := by
  simp

example a b c : {a, b} ⊆ ({a, b, c} : Finset ℝ) := by
  simp
```

…set_insert` (#28285)

I see some other similar theorems such as `List.cons_sublist_cons` and `Finset.cons_subset_cons` are already marked with `@[simp]` annotations. Doing this enables the following statements to be proved simpler with a single `simp`, which in turn makes proofs more easily found by proof search tactics:

```lean
example a b c : {a, b} ≤ ({a, b, c} : Multiset ℝ) := by
  simp

example a b : {a, b} ≤ ({a, a, b, b} : Multiset ℝ) := by
  simp

example a b c : {a, b} ⊆ ({a, b, c} : Finset ℝ) := by
  simp
```

…set_insert` (#28285)

I see some other similar theorems such as `List.cons_sublist_cons` and `Finset.cons_subset_cons` are already marked with `@[simp]` annotations. Doing this enables the following statements to be proved simpler with a single `simp`, which in turn makes proofs more easily found by proof search tactics:

```lean
example a b c : {a, b} ≤ ({a, b, c} : Multiset ℝ) := by
  simp

example a b : {a, b} ≤ ({a, a, b, b} : Multiset ℝ) := by
  simp

example a b c : {a, b} ⊆ ({a, b, c} : Finset ℝ) := by
  simp
```

…set_insert` (#28285)

I see some other similar theorems such as `List.cons_sublist_cons` and `Finset.cons_subset_cons` are already marked with `@[simp]` annotations. Doing this enables the following statements to be proved simpler with a single `simp`, which in turn makes proofs more easily found by proof search tactics:

```lean
example a b c : {a, b} ≤ ({a, b, c} : Multiset ℝ) := by
  simp

example a b : {a, b} ≤ ({a, a, b, b} : Multiset ℝ) := by
  simp

example a b c : {a, b} ⊆ ({a, b, c} : Finset ℝ) := by
  simp
```

…set_insert` (#28285)

I see some other similar theorems such as `List.cons_sublist_cons` and `Finset.cons_subset_cons` are already marked with `@[simp]` annotations. Doing this enables the following statements to be proved simpler with a single `simp`, which in turn makes proofs more easily found by proof search tactics:

```lean
example a b c : {a, b} ≤ ({a, b, c} : Multiset ℝ) := by
  simp

example a b : {a, b} ≤ ({a, a, b, b} : Multiset ℝ) := by
  simp

example a b c : {a, b} ⊆ ({a, b, c} : Finset ℝ) := by
  simp
```

* origin/master: (508 commits)
  feat(Logic/Basic): forall_and_index (leanprover-community#27737)
  feat(Algebra/intNorm): `x` divides `intNorm x` (leanprover-community#28021)
  feat(RingTheory/MvPolynomial/MonomialOrder): some lemmas about degree (leanprover-community#26000)
  chore: more elementary Motzkin polynomial proof (leanprover-community#28482)
  feat: e-seminormed monoid (leanprover-community#27385)
  feat(RingTheory): ` (⊥ : Ideal R) ^ n = ⊥` (leanprover-community#28171)
  fix(LinearAlgebra/Dimension/ErdosKaplansky): authorship (leanprover-community#28513)
  chore: golf entire `X_pow_eq_monomial` (leanprover-community#28504)
  feat(RingTheory): invertible modules and Picard group (leanprover-community#25337)
  chore: use delta `deriving` for leanprover-community#380 (leanprover-community#28498)
  feat: add bilinear maps for vector/matrix products (leanprover-community#28130)
  feat(Counterexamples): topologists' sine curve (leanprover-community#25833)
  feat(Analysis/Convex): doubly stochastic matrices have operator norm at most one (leanprover-community#28453)
  chore(Topology/Compactification): deprecate duplicate `ultrafilter_pure_injective` (leanprover-community#28436)
  feat: add `@[simp]` to `Multiset.cons_le_cons` and `Finset.insert_subset_insert` (leanprover-community#28285)
  feat: make `ring` work for semifields (leanprover-community#28494)
  feat: filtering lists and bounded quantifiers are primitive recursive (leanprover-community#26295)
  chore(Analysis/Analytic): split `Analytic.Basic` (leanprover-community#26270)
  refactor: tidy `mulVec` and `vecMul` lemmas about `•` (leanprover-community#28450)
  feat(Order/WellFounded): Acc and infinite descending chain (leanprover-community#28120)
  feat(NumberTheory/Padics): {Int,Rat}.padicValuation (leanprover-community#27667)
  chore(*): address a few timeout-related porting notes (leanprover-community#28483)
  feat(Algebra): toAlgebra_algebraMap (leanprover-community#28238)
  feat(Shrink): `IsCancelMul` instance (leanprover-community#28407)
  chore(Geometry): golf entire `chart_eq'` and `orthogonalProjection_orthogonalProjection` (leanprover-community#28485)
  feat: shifted geometric series and a `ProbabilityMeasure` version of `measure_iUnion_le` (leanprover-community#28087)
  chore(LinearAlgebra/PiTensorProduct): `rw` away use of `erw` in `lifts_zero` (leanprover-community#27554)
  feat(RingTheory): faithfully flat ring maps (leanprover-community#24530)
  chore(Geometry/RingedSpace): remove use of `erw` in `stalkSpecializes_stalkMap` (leanprover-community#27656)
  chore: add the Brownian motion project to downstream_repos.yml (leanprover-community#28459)
  feat(CategoryTheory/Sites/SheafOfTypes): composition of a sheaf with uliftFunctor is still a sheaf (leanprover-community#27816)
  feat(Valuation/DiscreteValuationRel): val relations with compatible valuations to Zm0 are IsDiscrete (leanprover-community#27213)
  chore(*): process a bunch of `aesop`-related porting notes (leanprover-community#28402)
  feat(CategoryTheory): abstract argument for the stability under transfinite compositions (leanprover-community#26030)
  chore: bump toolchain to v4.23.0-rc2 (leanprover-community#28454)
  chore(FieldTheory/Finite): fermat's little theorem in Nat form (leanprover-community#27962)
  feat(Combinatorics/SimpleGraph/Paths): add theorem `SimpleGraph.Walk.IsPath.concat` (leanprover-community#27582)
  feat(Slope): slope_pos_iff_of_le and related lemmas (leanprover-community#28039)
  feat: tactic analysis framework (leanprover-community#26683)
  chore(Data/EReal): deprecate `add_pos_of_nonneg_of_pos` and `add_ne_top_iff_of_ne_bot` (duplicates) (leanprover-community#28424)
  feat(MathlibTest/FieldSimp): add a few more tests (leanprover-community#28413)
  chore(RingTheory/HahnSeries): deprecate duplicate `orderTop_add_orderTop_le_orderTop_mul` (leanprover-community#28231)
  chore(AlgebraicGeometry/IdealSheaf): deprecate duplicate `AlgebraicGeometry.Scheme.IdealSheafData.Scheme.zeroLocus_radical` (leanprover-community#28202)
  feat(Algebra/Order): ArchimedeanClass ball (leanprover-community#27885)
  chore(Geometry/RingedSpace): remove use of `erw` in `isUnit_of_isUnit_germ` (leanprover-community#27660)
  feat(SkewMonoidAlgebra): coeff_mul lemmas (leanprover-community#27255)
  chore(LinearAlgebra): golf entire `isUnit_det` (leanprover-community#28438)
  chore(FieldTheory/IntermediateField): golf entire `coe_sum` and `coe_prod` (leanprover-community#28431)
  feat: separate linter error message for empty doc-strings (leanprover-community#27895)
  feat(RingTheory/PowerSeries/Binomial): add basic lemmas, golf (leanprover-community#27497)
  ...

…set_insert` (leanprover-community#28285)

I see some other similar theorems such as `List.cons_sublist_cons` and `Finset.cons_subset_cons` are already marked with `@[simp]` annotations. Doing this enables the following statements to be proved simpler with a single `simp`, which in turn makes proofs more easily found by proof search tactics:

```lean
example a b c : {a, b} ≤ ({a, b, c} : Multiset ℝ) := by
  simp

example a b : {a, b} ≤ ({a, a, b, b} : Multiset ℝ) := by
  simp

example a b c : {a, b} ⊆ ({a, b, c} : Finset ℝ) := by
  simp
```

…set_insert` (leanprover-community#28285)

I see some other similar theorems such as `List.cons_sublist_cons` and `Finset.cons_subset_cons` are already marked with `@[simp]` annotations. Doing this enables the following statements to be proved simpler with a single `simp`, which in turn makes proofs more easily found by proof search tactics:

```lean
example a b c : {a, b} ≤ ({a, b, c} : Multiset ℝ) := by
  simp

example a b : {a, b} ≤ ({a, a, b, b} : Multiset ℝ) := by
  simp

example a b c : {a, b} ⊆ ({a, b, c} : Finset ℝ) := by
  simp
```