chore(algebra/regular/*): generalisation linter (#13955)

src/algebra/regular/basic.lean

@@ -241,6 +241,18 @@ lemma not_is_regular_zero [nontrivial R] : ¬ is_regular (0 : R) :=
 
 end mul_zero_class
 
+section mul_one_class
+
+variable [mul_one_class R]
+
+/--  If multiplying by `1` on either side is the identity, `1` is regular. -/
+@[to_additive "If adding `0` on either side is the identity, `0` is regular."]
+lemma is_regular_one : is_regular (1 : R) :=
+⟨λ a b ab, (one_mul a).symm.trans (eq.trans ab (one_mul b)),
+  λ a b ab, (mul_one a).symm.trans (eq.trans ab (mul_one b))⟩
+
+end mul_one_class
+
 section comm_semigroup
 
 variable [comm_semigroup R]
@@ -259,12 +271,6 @@ section monoid
 
 variables [monoid R]
 
-/--  In a monoid, `1` is regular. -/
-@[to_additive "In an additive monoid, `0` is regular."]
-lemma is_regular_one : is_regular (1 : R) :=
-⟨λ a b ab, (one_mul a).symm.trans (eq.trans ab (one_mul b)),
-  λ a b ab, (mul_one a).symm.trans (eq.trans ab (mul_one b))⟩
-
 /-- An element admitting a left inverse is left-regular. -/
 @[to_additive "An element admitting a left additive opposite is add-left-regular."]
 lemma is_left_regular_of_mul_eq_one (h : b * a = 1) : is_left_regular a :=

src/algebra/regular/smul.lean

@@ -5,6 +5,7 @@ Authors: Damiano Testa
 -/
 import algebra.smul_with_zero
 import algebra.regular.basic
+
 /-!
 # Action of regular elements on a module
 
@@ -76,35 +77,22 @@ lemma is_left_regular [has_mul R] {a : R} (h : is_smul_regular R a) :
 lemma is_right_regular [has_mul R] {a : R} (h : is_smul_regular R (mul_opposite.op a)) :
   is_right_regular a := h
 
-end has_scalar
-
-section monoid
-
-variables [monoid R] [mul_action R M]
-
-variable (M)
-
-/-- One is `M`-regular always. -/
-@[simp] lemma one : is_smul_regular M (1 : R) :=
-λ a b ab, by rwa [one_smul, one_smul] at ab
-
-variable {M}
-
-lemma mul (ra : is_smul_regular M a) (rb : is_smul_regular M b) :
-  is_smul_regular M (a * b) :=
+lemma mul [has_mul R] [is_scalar_tower R R M]
+  (ra : is_smul_regular M a) (rb : is_smul_regular M b) : is_smul_regular M (a * b) :=
 ra.smul rb
 
-lemma of_mul (ab : is_smul_regular M (a * b)) :
+lemma of_mul [has_mul R] [is_scalar_tower R R M] (ab : is_smul_regular M (a * b)) :
   is_smul_regular M b :=
 by { rw ← smul_eq_mul at ab, exact ab.of_smul _ }
 
-@[simp] lemma mul_iff_right  (ha : is_smul_regular M a) :
+@[simp] lemma mul_iff_right [has_mul R] [is_scalar_tower R R M] (ha : is_smul_regular M a) :
   is_smul_regular M (a * b) ↔ is_smul_regular M b :=
 ⟨of_mul, ha.mul⟩
 
 /-- Two elements `a` and `b` are `M`-regular if and only if both products `a * b` and `b * a`
 are `M`-regular. -/
-lemma mul_and_mul_iff : is_smul_regular M (a * b) ∧ is_smul_regular M (b * a) ↔
+lemma mul_and_mul_iff [has_mul R] [is_scalar_tower R R M] :
+  is_smul_regular M (a * b) ∧ is_smul_regular M (b * a) ↔
   is_smul_regular M a ∧ is_smul_regular M b :=
 begin
   refine ⟨_, _⟩,
@@ -114,6 +102,24 @@ begin
     exact ⟨ha.mul hb, hb.mul ha⟩ }
 end
 
+end has_scalar
+
+section monoid
+
+variables [monoid R] [mul_action R M]
+
+variable (M)
+
+/-- One is `M`-regular always. -/
+@[simp] lemma one : is_smul_regular M (1 : R) :=
+λ a b ab, by rwa [one_smul, one_smul] at ab
+
+variable {M}
+
+/-- An element of `R` admitting a left inverse is `M`-regular. -/
+lemma of_mul_eq_one (h : a * b = 1) : is_smul_regular M b :=
+of_mul (by { rw h, exact one M })
+
 /-- Any power of an `M`-regular element is `M`-regular. -/
 lemma pow (n : ℕ) (ra : is_smul_regular M a) : is_smul_regular M (a ^ n) :=
 begin
@@ -133,10 +139,21 @@ end
 
 end monoid
 
+section monoid_smul
+
+variables [monoid S] [has_scalar R M] [has_scalar R S] [mul_action S M] [is_scalar_tower R S M]
+
+/-- An element of `S` admitting a left inverse in `R` is `M`-regular. -/
+lemma of_smul_eq_one (h : a • s = 1) : is_smul_regular M s :=
+of_smul a (by { rw h, exact one M })
+
+end monoid_smul
+
 section monoid_with_zero
 
-variables [monoid_with_zero R] [monoid_with_zero S] [has_zero M] [mul_action_with_zero R M]
-  [mul_action_with_zero R S] [mul_action_with_zero S M] [is_scalar_tower R S M]
+variables [monoid_with_zero R] [monoid_with_zero S] [has_zero M]
+          [mul_action_with_zero R M] [mul_action_with_zero R S] [mul_action_with_zero S M]
+          [is_scalar_tower R S M]
 
 /-- The element `0` is `M`-regular if and only if `M` is trivial. -/
 protected lemma subsingleton (h : is_smul_regular M (0 : R)) : subsingleton M :=
@@ -162,19 +179,11 @@ zero_iff_subsingleton.mpr sM
 lemma not_zero [nM : nontrivial M] : ¬ is_smul_regular M (0 : R) :=
 not_zero_iff.mpr nM
 
-/-- An element of `S` admitting a left inverse in `R` is `M`-regular. -/
-lemma of_smul_eq_one (h : a • s = 1) : is_smul_regular M s :=
-of_smul a (by { rw h, exact one M })
-
-/-- An element of `R` admitting a left inverse is `M`-regular. -/
-lemma of_mul_eq_one (h : a * b = 1) : is_smul_regular M b :=
-of_mul (by { rw h, exact one M })
-
 end monoid_with_zero
 
-section comm_monoid
+section comm_semigroup
 
-variables [comm_monoid R] [mul_action R M]
+variables [comm_semigroup R] [has_scalar R M] [is_scalar_tower R R M]
 
 /-- A product is `M`-regular if and only if the factors are. -/
 lemma mul_iff : is_smul_regular M (a * b) ↔
@@ -184,7 +193,7 @@ begin
   exact ⟨λ ab, ⟨ab, by rwa mul_comm⟩, λ rab, rab.1⟩
 end
 
-end comm_monoid
+end comm_semigroup
 
 end is_smul_regular
 
@@ -203,7 +212,9 @@ end
 
 end group
 
-variables [monoid_with_zero R] [has_zero M] [mul_action_with_zero R M]
+section units
+
+variables [monoid R] [mul_action R M]
 
 /-- Any element in `Rˣ` is `M`-regular. -/
 lemma units.is_smul_regular (a : Rˣ) : is_smul_regular M (a : R) :=
@@ -215,3 +226,5 @@ begin
   rcases ua with ⟨a, rfl⟩,
   exact a.is_smul_regular M
 end
+
+end units