mathlib commit https://github.com/leanprover-community/mathlib/commit/65a1391a0106c9204fe45bc73a039f056558cb83

@@ -60,7 +60,7 @@ theorem FiniteField.isSquare_two_iff :
     simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
       imp_false, Classical.not_not]
   all_goals
-    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h 
+    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h
     have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
     revert h₁ h
     generalize Fintype.card F % 8 = n
@@ -94,7 +94,7 @@ theorem FiniteField.isSquare_neg_two_iff :
     simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
       imp_false, Classical.not_not]
   all_goals
-    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h 
+    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h
     have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
     revert h₁ h
     generalize Fintype.card F % 8 = n
@@ -123,7 +123,7 @@ theorem quadraticChar_card_card [DecidableEq F] (hF : ringChar F ≠ 2) {F' : Ty
     exact Ring.neg_one_ne_one_of_char_ne_two hF'
   have hχ₂ : χ.is_quadratic := is_quadratic.comp (quadraticChar_isQuadratic F) _
   have h := Char.card_pow_card hχ₁ hχ₂ h hF'
-  rw [← quadraticChar_eq_pow_of_char_ne_two' hF'] at h 
+  rw [← quadraticChar_eq_pow_of_char_ne_two' hF'] at h
   exact
     (is_quadratic.eq_of_eq_coe (quadraticChar_isQuadratic F') (quadraticChar_isQuadratic F) hF'
         h).symm
@@ -140,7 +140,7 @@ theorem quadraticChar_odd_prime [DecidableEq F] (hF : ringChar F ≠ 2) {p : ℕ
   have h :=
     quadraticChar_card_card hF (ne_of_eq_of_ne (ring_char_zmod_n p) hp₁)
       (ne_of_eq_of_ne (ring_char_zmod_n p) hp₂.symm)
-  rwa [card p] at h 
+  rwa [card p] at h
 #align quadratic_char_odd_prime quadraticChar_odd_prime
 -/
 

mathlib commit https://github.com/leanprover-community/mathlib/commit/65a1391a0106c9204fe45bc73a039f056558cb83

@@ -46,7 +46,25 @@ theorem quadraticChar_two [DecidableEq F] (hF : ringChar F ≠ 2) :
 #print FiniteField.isSquare_two_iff /-
 /-- `2` is a square in `F` iff `#F` is not congruent to `3` or `5` mod `8`. -/
 theorem FiniteField.isSquare_two_iff :
-    IsSquare (2 : F) ↔ Fintype.card F % 8 ≠ 3 ∧ Fintype.card F % 8 ≠ 5 := by classical
+    IsSquare (2 : F) ↔ Fintype.card F % 8 ≠ 3 ∧ Fintype.card F % 8 ≠ 5 := by
+  classical
+  by_cases hF : ringChar F = 2
+  focus
+    have h := FiniteField.even_card_of_char_two hF
+    simp only [FiniteField.isSquare_of_char_two hF, true_iff_iff]
+  rotate_left
+  focus
+    have h := FiniteField.odd_card_of_char_ne_two hF
+    rw [← quadraticChar_one_iff_isSquare (Ring.two_ne_zero hF), quadraticChar_two hF,
+      χ₈_nat_eq_if_mod_eight]
+    simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
+      imp_false, Classical.not_not]
+  all_goals
+    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h 
+    have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
+    revert h₁ h
+    generalize Fintype.card F % 8 = n
+    decide!
 #align finite_field.is_square_two_iff FiniteField.isSquare_two_iff
 -/
 
@@ -62,7 +80,25 @@ theorem quadraticChar_neg_two [DecidableEq F] (hF : ringChar F ≠ 2) :
 #print FiniteField.isSquare_neg_two_iff /-
 /-- `-2` is a square in `F` iff `#F` is not congruent to `5` or `7` mod `8`. -/
 theorem FiniteField.isSquare_neg_two_iff :
-    IsSquare (-2 : F) ↔ Fintype.card F % 8 ≠ 5 ∧ Fintype.card F % 8 ≠ 7 := by classical
+    IsSquare (-2 : F) ↔ Fintype.card F % 8 ≠ 5 ∧ Fintype.card F % 8 ≠ 7 := by
+  classical
+  by_cases hF : ringChar F = 2
+  focus
+    have h := FiniteField.even_card_of_char_two hF
+    simp only [FiniteField.isSquare_of_char_two hF, true_iff_iff]
+  rotate_left
+  focus
+    have h := FiniteField.odd_card_of_char_ne_two hF
+    rw [← quadraticChar_one_iff_isSquare (neg_ne_zero.mpr (Ring.two_ne_zero hF)),
+      quadraticChar_neg_two hF, χ₈'_nat_eq_if_mod_eight]
+    simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
+      imp_false, Classical.not_not]
+  all_goals
+    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h 
+    have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
+    revert h₁ h
+    generalize Fintype.card F % 8 = n
+    decide!
 #align finite_field.is_square_neg_two_iff FiniteField.isSquare_neg_two_iff
 -/
 
@@ -115,6 +151,21 @@ theorem FiniteField.isSquare_odd_prime_iff (hF : ringChar F ≠ 2) {p : ℕ} [Fa
     (hp : p ≠ 2) :
     IsSquare (p : F) ↔ quadraticChar (ZMod p) (χ₄ (Fintype.card F) * Fintype.card F) ≠ -1 := by
   classical
+  by_cases hFp : ringChar F = p
+  · rw [show (p : F) = 0 by rw [← hFp]; exact ringChar.Nat.cast_ringChar]
+    simp only [isSquare_zero, Ne.def, true_iff_iff, map_mul]
+    obtain ⟨n, _, hc⟩ := FiniteField.card F (ringChar F)
+    have hchar : ringChar F = ringChar (ZMod p) := by rw [hFp]; exact (ring_char_zmod_n p).symm
+    conv =>
+      congr
+      lhs
+      congr
+      skip
+      rw [hc, Nat.cast_pow, map_pow, hchar, map_ring_char]
+    simp only [zero_pow n.pos, MulZeroClass.mul_zero, zero_eq_neg, one_ne_zero, not_false_iff]
+  · rw [← Iff.not_left (@quadraticChar_neg_one_iff_not_isSquare F _ _ _ _),
+      quadraticChar_odd_prime hF hp]
+    exact hFp
 #align finite_field.is_square_odd_prime_iff FiniteField.isSquare_odd_prime_iff
 -/
 

mathlib commit https://github.com/leanprover-community/mathlib/commit/65a1391a0106c9204fe45bc73a039f056558cb83

@@ -46,25 +46,7 @@ theorem quadraticChar_two [DecidableEq F] (hF : ringChar F ≠ 2) :
 #print FiniteField.isSquare_two_iff /-
 /-- `2` is a square in `F` iff `#F` is not congruent to `3` or `5` mod `8`. -/
 theorem FiniteField.isSquare_two_iff :
-    IsSquare (2 : F) ↔ Fintype.card F % 8 ≠ 3 ∧ Fintype.card F % 8 ≠ 5 := by
-  classical
-  by_cases hF : ringChar F = 2
-  focus
-    have h := FiniteField.even_card_of_char_two hF
-    simp only [FiniteField.isSquare_of_char_two hF, true_iff_iff]
-  rotate_left
-  focus
-    have h := FiniteField.odd_card_of_char_ne_two hF
-    rw [← quadraticChar_one_iff_isSquare (Ring.two_ne_zero hF), quadraticChar_two hF,
-      χ₈_nat_eq_if_mod_eight]
-    simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
-      imp_false, Classical.not_not]
-  all_goals
-    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h 
-    have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
-    revert h₁ h
-    generalize Fintype.card F % 8 = n
-    decide!
+    IsSquare (2 : F) ↔ Fintype.card F % 8 ≠ 3 ∧ Fintype.card F % 8 ≠ 5 := by classical
 #align finite_field.is_square_two_iff FiniteField.isSquare_two_iff
 -/
 
@@ -80,25 +62,7 @@ theorem quadraticChar_neg_two [DecidableEq F] (hF : ringChar F ≠ 2) :
 #print FiniteField.isSquare_neg_two_iff /-
 /-- `-2` is a square in `F` iff `#F` is not congruent to `5` or `7` mod `8`. -/
 theorem FiniteField.isSquare_neg_two_iff :
-    IsSquare (-2 : F) ↔ Fintype.card F % 8 ≠ 5 ∧ Fintype.card F % 8 ≠ 7 := by
-  classical
-  by_cases hF : ringChar F = 2
-  focus
-    have h := FiniteField.even_card_of_char_two hF
-    simp only [FiniteField.isSquare_of_char_two hF, true_iff_iff]
-  rotate_left
-  focus
-    have h := FiniteField.odd_card_of_char_ne_two hF
-    rw [← quadraticChar_one_iff_isSquare (neg_ne_zero.mpr (Ring.two_ne_zero hF)),
-      quadraticChar_neg_two hF, χ₈'_nat_eq_if_mod_eight]
-    simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
-      imp_false, Classical.not_not]
-  all_goals
-    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h 
-    have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
-    revert h₁ h
-    generalize Fintype.card F % 8 = n
-    decide!
+    IsSquare (-2 : F) ↔ Fintype.card F % 8 ≠ 5 ∧ Fintype.card F % 8 ≠ 7 := by classical
 #align finite_field.is_square_neg_two_iff FiniteField.isSquare_neg_two_iff
 -/
 
@@ -151,21 +115,6 @@ theorem FiniteField.isSquare_odd_prime_iff (hF : ringChar F ≠ 2) {p : ℕ} [Fa
     (hp : p ≠ 2) :
     IsSquare (p : F) ↔ quadraticChar (ZMod p) (χ₄ (Fintype.card F) * Fintype.card F) ≠ -1 := by
   classical
-  by_cases hFp : ringChar F = p
-  · rw [show (p : F) = 0 by rw [← hFp]; exact ringChar.Nat.cast_ringChar]
-    simp only [isSquare_zero, Ne.def, true_iff_iff, map_mul]
-    obtain ⟨n, _, hc⟩ := FiniteField.card F (ringChar F)
-    have hchar : ringChar F = ringChar (ZMod p) := by rw [hFp]; exact (ring_char_zmod_n p).symm
-    conv =>
-      congr
-      lhs
-      congr
-      skip
-      rw [hc, Nat.cast_pow, map_pow, hchar, map_ring_char]
-    simp only [zero_pow n.pos, MulZeroClass.mul_zero, zero_eq_neg, one_ne_zero, not_false_iff]
-  · rw [← Iff.not_left (@quadraticChar_neg_one_iff_not_isSquare F _ _ _ _),
-      quadraticChar_odd_prime hF hp]
-    exact hFp
 #align finite_field.is_square_odd_prime_iff FiniteField.isSquare_odd_prime_iff
 -/
 

mathlib commit https://github.com/leanprover-community/mathlib/commit/ce64cd319bb6b3e82f31c2d38e79080d377be451

@@ -3,8 +3,8 @@ Copyright (c) 2022 Michael Stoll. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Michael Stoll
 -/
-import Mathbin.NumberTheory.LegendreSymbol.QuadraticChar.Basic
-import Mathbin.NumberTheory.LegendreSymbol.GaussSum
+import NumberTheory.LegendreSymbol.QuadraticChar.Basic
+import NumberTheory.LegendreSymbol.GaussSum
 
 #align_import number_theory.legendre_symbol.quadratic_char.gauss_sum from "leanprover-community/mathlib"@"08b63ab58a6ec1157ebeafcbbe6c7a3fb3c9f6d5"
 

mathlib commit https://github.com/leanprover-community/mathlib/commit/8ea5598db6caeddde6cb734aa179cc2408dbd345

@@ -2,15 +2,12 @@
 Copyright (c) 2022 Michael Stoll. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Michael Stoll
-
-! This file was ported from Lean 3 source module number_theory.legendre_symbol.quadratic_char.gauss_sum
-! leanprover-community/mathlib commit 08b63ab58a6ec1157ebeafcbbe6c7a3fb3c9f6d5
-! Please do not edit these lines, except to modify the commit id
-! if you have ported upstream changes.
 -/
 import Mathbin.NumberTheory.LegendreSymbol.QuadraticChar.Basic
 import Mathbin.NumberTheory.LegendreSymbol.GaussSum
 
+#align_import number_theory.legendre_symbol.quadratic_char.gauss_sum from "leanprover-community/mathlib"@"08b63ab58a6ec1157ebeafcbbe6c7a3fb3c9f6d5"
+
 /-!
 # Quadratic characters of finite fields
 

mathlib commit https://github.com/leanprover-community/mathlib/commit/9240e8be927a0955b9a82c6c85ef499ee3a626b8

@@ -4,7 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Michael Stoll
 
 ! This file was ported from Lean 3 source module number_theory.legendre_symbol.quadratic_char.gauss_sum
-! leanprover-community/mathlib commit 5b2fe80501ff327b9109fb09b7cc8c325cd0d7d9
+! leanprover-community/mathlib commit 08b63ab58a6ec1157ebeafcbbe6c7a3fb3c9f6d5
 ! Please do not edit these lines, except to modify the commit id
 ! if you have ported upstream changes.
 -/
@@ -14,6 +14,9 @@ import Mathbin.NumberTheory.LegendreSymbol.GaussSum
 /-!
 # Quadratic characters of finite fields
 
+> THIS FILE IS SYNCHRONIZED WITH MATHLIB4.
+> Any changes to this file require a corresponding PR to mathlib4.
+
 Further facts relying on Gauss sums.
 
 -/

mathlib commit https://github.com/leanprover-community/mathlib/commit/fdc286cc6967a012f41b87f76dcd2797b53152af

@@ -34,13 +34,16 @@ open ZMod MulChar
 
 variable {F : Type _} [Field F] [Fintype F]
 
+#print quadraticChar_two /-
 /-- The value of the quadratic character at `2` -/
 theorem quadraticChar_two [DecidableEq F] (hF : ringChar F ≠ 2) :
     quadraticChar F 2 = χ₈ (Fintype.card F) :=
   IsQuadratic.eq_of_eq_coe (quadraticChar_isQuadratic F) isQuadratic_χ₈ hF
     ((quadraticChar_eq_pow_of_char_ne_two' hF 2).trans (FiniteField.two_pow_card hF))
 #align quadratic_char_two quadraticChar_two
+-/
 
+#print FiniteField.isSquare_two_iff /-
 /-- `2` is a square in `F` iff `#F` is not congruent to `3` or `5` mod `8`. -/
 theorem FiniteField.isSquare_two_iff :
     IsSquare (2 : F) ↔ Fintype.card F % 8 ≠ 3 ∧ Fintype.card F % 8 ≠ 5 := by
@@ -63,14 +66,18 @@ theorem FiniteField.isSquare_two_iff :
     generalize Fintype.card F % 8 = n
     decide!
 #align finite_field.is_square_two_iff FiniteField.isSquare_two_iff
+-/
 
+#print quadraticChar_neg_two /-
 /-- The value of the quadratic character at `-2` -/
 theorem quadraticChar_neg_two [DecidableEq F] (hF : ringChar F ≠ 2) :
     quadraticChar F (-2) = χ₈' (Fintype.card F) := by
   rw [(by norm_num : (-2 : F) = -1 * 2), map_mul, χ₈'_eq_χ₄_mul_χ₈, quadraticChar_neg_one hF,
     quadraticChar_two hF, @cast_nat_cast _ (ZMod 4) _ _ _ (by norm_num : 4 ∣ 8)]
 #align quadratic_char_neg_two quadraticChar_neg_two
+-/
 
+#print FiniteField.isSquare_neg_two_iff /-
 /-- `-2` is a square in `F` iff `#F` is not congruent to `5` or `7` mod `8`. -/
 theorem FiniteField.isSquare_neg_two_iff :
     IsSquare (-2 : F) ↔ Fintype.card F % 8 ≠ 5 ∧ Fintype.card F % 8 ≠ 7 := by
@@ -93,7 +100,9 @@ theorem FiniteField.isSquare_neg_two_iff :
     generalize Fintype.card F % 8 = n
     decide!
 #align finite_field.is_square_neg_two_iff FiniteField.isSquare_neg_two_iff
+-/
 
+#print quadraticChar_card_card /-
 /-- The relation between the values of the quadratic character of one field `F` at the
 cardinality of another field `F'` and of the quadratic character of `F'` at the cardinality
 of `F`. -/
@@ -119,7 +128,9 @@ theorem quadraticChar_card_card [DecidableEq F] (hF : ringChar F ≠ 2) {F' : Ty
     (is_quadratic.eq_of_eq_coe (quadraticChar_isQuadratic F') (quadraticChar_isQuadratic F) hF'
         h).symm
 #align quadratic_char_card_card quadraticChar_card_card
+-/
 
+#print quadraticChar_odd_prime /-
 /-- The value of the quadratic character at an odd prime `p` different from `ring_char F`. -/
 theorem quadraticChar_odd_prime [DecidableEq F] (hF : ringChar F ≠ 2) {p : ℕ} [Fact p.Prime]
     (hp₁ : p ≠ 2) (hp₂ : ringChar F ≠ p) :
@@ -131,7 +142,9 @@ theorem quadraticChar_odd_prime [DecidableEq F] (hF : ringChar F ≠ 2) {p : ℕ
       (ne_of_eq_of_ne (ring_char_zmod_n p) hp₂.symm)
   rwa [card p] at h 
 #align quadratic_char_odd_prime quadraticChar_odd_prime
+-/
 
+#print FiniteField.isSquare_odd_prime_iff /-
 /-- An odd prime `p` is a square in `F` iff the quadratic character of `zmod p` does not
 take the value `-1` on `χ₄(#F) * #F`. -/
 theorem FiniteField.isSquare_odd_prime_iff (hF : ringChar F ≠ 2) {p : ℕ} [Fact p.Prime]
@@ -154,6 +167,7 @@ theorem FiniteField.isSquare_odd_prime_iff (hF : ringChar F ≠ 2) {p : ℕ} [Fa
       quadraticChar_odd_prime hF hp]
     exact hFp
 #align finite_field.is_square_odd_prime_iff FiniteField.isSquare_odd_prime_iff
+-/
 
 end SpecialValues
 

mathlib commit https://github.com/leanprover-community/mathlib/commit/893964fc28cefbcffc7cb784ed00a2895b4e65cf

Now that I am defining NNRat.cast, I want a definitive answer to this naming issue. Plenty of lemmas in mathlib already use natCast/intCast/ratCast over nat_cast/int_cast/rat_cast, and this matches with the general expectation that underscore-separated name parts correspond to a single declaration.

@@ -65,7 +65,7 @@ theorem FiniteField.isSquare_two_iff :
 theorem quadraticChar_neg_two [DecidableEq F] (hF : ringChar F ≠ 2) :
     quadraticChar F (-2) = χ₈' (Fintype.card F) := by
   rw [(by norm_num : (-2 : F) = -1 * 2), map_mul, χ₈'_eq_χ₄_mul_χ₈, quadraticChar_neg_one hF,
-    quadraticChar_two hF, @cast_nat_cast _ (ZMod 4) _ _ _ (by decide : 4 ∣ 8)]
+    quadraticChar_two hF, @cast_natCast _ (ZMod 4) _ _ _ (by decide : 4 ∣ 8)]
 #align quadratic_char_neg_two quadraticChar_neg_two
 
 /-- `-2` is a square in `F` iff `#F` is not congruent to `5` or `7` mod `8`. -/

@@ -51,7 +51,7 @@ theorem FiniteField.isSquare_two_iff :
     have h := FiniteField.odd_card_of_char_ne_two hF
     rw [← quadraticChar_one_iff_isSquare (Ring.two_ne_zero hF), quadraticChar_two hF,
       χ₈_nat_eq_if_mod_eight]
-    simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
+    simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne, (by decide : (-1 : ℤ) ≠ 1),
       imp_false, Classical.not_not]
   all_goals
     rw [← Nat.mod_mod_of_dvd _ (by decide : 2 ∣ 8)] at h
@@ -81,7 +81,7 @@ theorem FiniteField.isSquare_neg_two_iff :
     have h := FiniteField.odd_card_of_char_ne_two hF
     rw [← quadraticChar_one_iff_isSquare (neg_ne_zero.mpr (Ring.two_ne_zero hF)),
       quadraticChar_neg_two hF, χ₈'_nat_eq_if_mod_eight]
-    simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
+    simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne, (by decide : (-1 : ℤ) ≠ 1),
       imp_false, Classical.not_not]
   all_goals
     rw [← Nat.mod_mod_of_dvd _ (by decide : 2 ∣ 8)] at h
@@ -105,7 +105,7 @@ theorem quadraticChar_card_card [DecidableEq F] (hF : ringChar F ≠ 2) {F' : Ty
       contrapose ha
       exact ne_of_eq_of_ne (map_nonunit (quadraticChar F) ha) (mt zero_eq_neg.mp one_ne_zero)
     use hu.unit
-    simp only [χ, IsUnit.unit_spec, ringHomComp_apply, eq_intCast, Ne.def, ha]
+    simp only [χ, IsUnit.unit_spec, ringHomComp_apply, eq_intCast, Ne, ha]
     rw [Int.cast_neg, Int.cast_one]
     exact Ring.neg_one_ne_one_of_char_ne_two hF'
   have hχ₂ : χ.IsQuadratic := IsQuadratic.comp (quadraticChar_isQuadratic F) _
@@ -133,7 +133,7 @@ theorem FiniteField.isSquare_odd_prime_iff (hF : ringChar F ≠ 2) {p : ℕ} [Fa
   classical
   by_cases hFp : ringChar F = p
   · rw [show (p : F) = 0 by rw [← hFp]; exact ringChar.Nat.cast_ringChar]
-    simp only [isSquare_zero, Ne.def, true_iff_iff, map_mul]
+    simp only [isSquare_zero, Ne, true_iff_iff, map_mul]
     obtain ⟨n, _, hc⟩ := FiniteField.card F (ringChar F)
     have hchar : ringChar F = ringChar (ZMod p) := by rw [hFp]; exact (ringChar_zmod_n p).symm
     conv => enter [1, 1, 2]; rw [hc, Nat.cast_pow, map_pow, hchar, map_ringChar]

Classifies by adding issue number #11043 to porting notes claiming:

was decide!

@@ -58,7 +58,7 @@ theorem FiniteField.isSquare_two_iff :
     have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
     revert h₁ h
     generalize Fintype.card F % 8 = n
-    intros; interval_cases n <;> simp_all -- Porting note: was `decide!`
+    intros; interval_cases n <;> simp_all -- Porting note (#11043): was `decide!`
 #align finite_field.is_square_two_iff FiniteField.isSquare_two_iff
 
 /-- The value of the quadratic character at `-2` -/
@@ -88,7 +88,7 @@ theorem FiniteField.isSquare_neg_two_iff :
     have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
     revert h₁ h
     generalize Fintype.card F % 8 = n
-    intros; interval_cases n <;> simp_all -- Porting note: was `decide!`
+    intros; interval_cases n <;> simp_all -- Porting note (#11043): was `decide!`
 #align finite_field.is_square_neg_two_iff FiniteField.isSquare_neg_two_iff
 
 /-- The relation between the values of the quadratic character of one field `F` at the

Co-authored-by: Patrick Massot <patrickmassot@free.fr> Co-authored-by: Scott Morrison <scott.morrison@gmail.com>

@@ -105,7 +105,7 @@ theorem quadraticChar_card_card [DecidableEq F] (hF : ringChar F ≠ 2) {F' : Ty
       contrapose ha
       exact ne_of_eq_of_ne (map_nonunit (quadraticChar F) ha) (mt zero_eq_neg.mp one_ne_zero)
     use hu.unit
-    simp only [IsUnit.unit_spec, ringHomComp_apply, eq_intCast, Ne.def, ha]
+    simp only [χ, IsUnit.unit_spec, ringHomComp_apply, eq_intCast, Ne.def, ha]
     rw [Int.cast_neg, Int.cast_one]
     exact Ring.neg_one_ne_one_of_char_ne_two hF'
   have hχ₂ : χ.IsQuadratic := IsQuadratic.comp (quadraticChar_isQuadratic F) _

This involves moving lemmas from Algebra.GroupPower.Ring to Algebra.GroupWithZero.Basic and changing some 0 < n assumptions to n ≠ 0.

From LeanAPAP

@@ -137,7 +137,7 @@ theorem FiniteField.isSquare_odd_prime_iff (hF : ringChar F ≠ 2) {p : ℕ} [Fa
     obtain ⟨n, _, hc⟩ := FiniteField.card F (ringChar F)
     have hchar : ringChar F = ringChar (ZMod p) := by rw [hFp]; exact (ringChar_zmod_n p).symm
     conv => enter [1, 1, 2]; rw [hc, Nat.cast_pow, map_pow, hchar, map_ringChar]
-    simp only [zero_pow n.pos, mul_zero, zero_eq_neg, one_ne_zero, not_false_iff]
+    simp only [zero_pow n.ne_zero, mul_zero, zero_eq_neg, one_ne_zero, not_false_iff]
   · rw [← Iff.not_left (@quadraticChar_neg_one_iff_not_isSquare F _ _ _ _),
       quadraticChar_odd_prime hF hp]
     exact hFp

PR contents

This is the supremum of

• #8284
• #8056
• #8023
• #8332
• #8226 (already approved)
• #7834 (already approved)

along with some minor fixes from failures on nightly-testing as Mathlib master is merged into it.

Note that some PRs for changes that are already compatible with the current toolchain and will be necessary have already been split out: #8380.

I am hopeful that in future we will be able to progressively merge adaptation PRs into a bump/v4.X.0 branch, so we never end up with a "big merge" like this. However one of these adaptation PRs (#8056) predates my new scheme for combined CI, and it wasn't possible to keep that PR viable in the meantime.

Lean PRs involved in this bump

In particular this includes adjustments for the Lean PRs

• leanprover/lean4#2778
• leanprover/lean4#2790
• leanprover/lean4#2783
• leanprover/lean4#2825
• leanprover/lean4#2722

leanprover/lean4#2778

We can get rid of all the

local macro_rules | `($x ^ $y) => `(HPow.hPow $x $y) -- Porting note: See issue [lean4#2220](https://github.com/leanprover/lean4/pull/2220)

macros across Mathlib (and in any projects that want to write natural number powers of reals).

leanprover/lean4#2722

Changes the default behaviour of simp to (config := {decide := false}). This makes simp (and consequentially norm_num) less powerful, but also more consistent, and less likely to blow up in long failures. This requires a variety of changes: changing some previously by simp or norm_num to decide or rfl, or adding (config := {decide := true}).

leanprover/lean4#2783

This changed the behaviour of simp so that simp [f] will only unfold "fully applied" occurrences of f. The old behaviour can be recovered with simp (config := { unfoldPartialApp := true }). We may in future add a syntax for this, e.g. simp [!f]; please provide feedback! In the meantime, we have made the following changes:

• switching to using explicit lemmas that have the intended level of application
• (config := { unfoldPartialApp := true }) in some places, to recover the old behaviour
• Using @[eqns] to manually adjust the equation lemmas for a particular definition, recovering the old behaviour just for that definition. See #8371, where we do this for Function.comp and Function.flip.

This change in Lean may require further changes down the line (e.g. adding the !f syntax, and/or upstreaming the special treatment for Function.comp and Function.flip, and/or removing this special treatment). Please keep an open and skeptical mind about these changes!

Co-authored-by: leanprover-community-mathlib4-bot <leanprover-community-mathlib4-bot@users.noreply.github.com> Co-authored-by: Scott Morrison <scott.morrison@gmail.com> Co-authored-by: Eric Wieser <wieser.eric@gmail.com> Co-authored-by: Mauricio Collares <mauricio@collares.org>

@@ -54,7 +54,7 @@ theorem FiniteField.isSquare_two_iff :
     simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
       imp_false, Classical.not_not]
   all_goals
-    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h
+    rw [← Nat.mod_mod_of_dvd _ (by decide : 2 ∣ 8)] at h
     have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
     revert h₁ h
     generalize Fintype.card F % 8 = n
@@ -65,7 +65,7 @@ theorem FiniteField.isSquare_two_iff :
 theorem quadraticChar_neg_two [DecidableEq F] (hF : ringChar F ≠ 2) :
     quadraticChar F (-2) = χ₈' (Fintype.card F) := by
   rw [(by norm_num : (-2 : F) = -1 * 2), map_mul, χ₈'_eq_χ₄_mul_χ₈, quadraticChar_neg_one hF,
-    quadraticChar_two hF, @cast_nat_cast _ (ZMod 4) _ _ _ (by norm_num : 4 ∣ 8)]
+    quadraticChar_two hF, @cast_nat_cast _ (ZMod 4) _ _ _ (by decide : 4 ∣ 8)]
 #align quadratic_char_neg_two quadraticChar_neg_two
 
 /-- `-2` is a square in `F` iff `#F` is not congruent to `5` or `7` mod `8`. -/
@@ -84,7 +84,7 @@ theorem FiniteField.isSquare_neg_two_iff :
     simp only [h, Nat.one_ne_zero, if_false, ite_eq_left_iff, Ne.def, (by decide : (-1 : ℤ) ≠ 1),
       imp_false, Classical.not_not]
   all_goals
-    rw [← Nat.mod_mod_of_dvd _ (by norm_num : 2 ∣ 8)] at h
+    rw [← Nat.mod_mod_of_dvd _ (by decide : 2 ∣ 8)] at h
     have h₁ := Nat.mod_lt (Fintype.card F) (by decide : 0 < 8)
     revert h₁ h
     generalize Fintype.card F % 8 = n

Search&replace MulZeroClass.mul_zero -> mul_zero, MulZeroClass.zero_mul -> zero_mul.

These were introduced by Mathport, as the full name of mul_zero is actually MulZeroClass.mul_zero (it's exported with the short name).

@@ -137,7 +137,7 @@ theorem FiniteField.isSquare_odd_prime_iff (hF : ringChar F ≠ 2) {p : ℕ} [Fa
     obtain ⟨n, _, hc⟩ := FiniteField.card F (ringChar F)
     have hchar : ringChar F = ringChar (ZMod p) := by rw [hFp]; exact (ringChar_zmod_n p).symm
     conv => enter [1, 1, 2]; rw [hc, Nat.cast_pow, map_pow, hchar, map_ringChar]
-    simp only [zero_pow n.pos, MulZeroClass.mul_zero, zero_eq_neg, one_ne_zero, not_false_iff]
+    simp only [zero_pow n.pos, mul_zero, zero_eq_neg, one_ne_zero, not_false_iff]
   · rw [← Iff.not_left (@quadraticChar_neg_one_iff_not_isSquare F _ _ _ _),
       quadraticChar_odd_prime hF hp]
     exact hFp

We remove all possible occurences of Type _ and Sort _ in favor of Type* and Sort*.

This has nice performance benefits.

@@ -29,7 +29,7 @@ section SpecialValues
 
 open ZMod MulChar
 
-variable {F : Type _} [Field F] [Fintype F]
+variable {F : Type*} [Field F] [Fintype F]
 
 /-- The value of the quadratic character at `2` -/
 theorem quadraticChar_two [DecidableEq F] (hF : ringChar F ≠ 2) :
@@ -94,7 +94,7 @@ theorem FiniteField.isSquare_neg_two_iff :
 /-- The relation between the values of the quadratic character of one field `F` at the
 cardinality of another field `F'` and of the quadratic character of `F'` at the cardinality
 of `F`. -/
-theorem quadraticChar_card_card [DecidableEq F] (hF : ringChar F ≠ 2) {F' : Type _} [Field F']
+theorem quadraticChar_card_card [DecidableEq F] (hF : ringChar F ≠ 2) {F' : Type*} [Field F']
     [Fintype F'] [DecidableEq F'] (hF' : ringChar F' ≠ 2) (h : ringChar F' ≠ ringChar F) :
     quadraticChar F (Fintype.card F') =
     quadraticChar F' (quadraticChar F (-1) * Fintype.card F) := by

• depends on: #5966

Co-authored-by: Eric Wieser <wieser.eric@gmail.com> Co-authored-by: Scott Morrison <scott.morrison@gmail.com>

@@ -2,15 +2,12 @@
 Copyright (c) 2022 Michael Stoll. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Michael Stoll
-
-! This file was ported from Lean 3 source module number_theory.legendre_symbol.quadratic_char.gauss_sum
-! leanprover-community/mathlib commit 5b2fe80501ff327b9109fb09b7cc8c325cd0d7d9
-! Please do not edit these lines, except to modify the commit id
-! if you have ported upstream changes.
 -/
 import Mathlib.NumberTheory.LegendreSymbol.QuadraticChar.Basic
 import Mathlib.NumberTheory.LegendreSymbol.GaussSum
 
+#align_import number_theory.legendre_symbol.quadratic_char.gauss_sum from "leanprover-community/mathlib"@"5b2fe80501ff327b9109fb09b7cc8c325cd0d7d9"
+
 /-!
 # Quadratic characters of finite fields
 

@@ -129,7 +129,7 @@ theorem quadraticChar_odd_prime [DecidableEq F] (hF : ringChar F ≠ 2) {p : ℕ
 #align quadratic_char_odd_prime quadraticChar_odd_prime
 
 /-- An odd prime `p` is a square in `F` iff the quadratic character of `ZMod p` does not
-take the value `-1` on `χ₄(#F) * #F`. -/
+take the value `-1` on `χ₄#F * #F`. -/
 theorem FiniteField.isSquare_odd_prime_iff (hF : ringChar F ≠ 2) {p : ℕ} [Fact p.Prime]
     (hp : p ≠ 2) :
     IsSquare (p : F) ↔ quadraticChar (ZMod p) (χ₄ (Fintype.card F) * Fintype.card F) ≠ -1 := by