Theorem: Pi.mulSingle_mul_mulSingle_eq_mulSingle_mul_mulSingle
File: Mathlib/Algebra/Group/Pi.lean

tactic: refine' ⟨fun h => _, _⟩
state_before: ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
⊢ mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v ↔
    k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: have hk := congr_fun h k
state_before: case refine'_1
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: have hl := congr_fun h l
state_before: case refine'_1
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v
hk : (mulSingle k u * mulSingle l v) k = (mulSingle m u * mulSingle n v) k
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: have hm := (congr_fun h m).symm
state_before: case refine'_1
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v
hk : (mulSingle k u * mulSingle l v) k = (mulSingle m u * mulSingle n v) k
hl : (mulSingle k u * mulSingle l v) l = (mulSingle m u * mulSingle n v) l
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: have hn := (congr_fun h n).symm
state_before: case refine'_1
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v
hk : (mulSingle k u * mulSingle l v) k = (mulSingle m u * mulSingle n v) k
hl : (mulSingle k u * mulSingle l v) l = (mulSingle m u * mulSingle n v) l
hm : (mulSingle m u * mulSingle n v) m = (mulSingle k u * mulSingle l v) m
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: simp only [mul_apply, mulSingle_apply, if_pos rfl] at hk hl hm hn
state_before: case refine'_1
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v
hk : (mulSingle k u * mulSingle l v) k = (mulSingle m u * mulSingle n v) k
hl : (mulSingle k u * mulSingle l v) l = (mulSingle m u * mulSingle n v) l
hm : (mulSingle m u * mulSingle n v) m = (mulSingle k u * mulSingle l v) m
hn : (mulSingle m u * mulSingle n v) n = (mulSingle k u * mulSingle l v) n
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: rcases eq_or_ne k m with (rfl | hkm)
state_before: case refine'_1
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v
hk : ((if True then u else 1) * if k = l then v else 1) = (if k = m then u else 1) * if k = n then v else 1
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = m then u else 1) * if l = n then v else 1
hm : ((if True then u else 1) * if m = n then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hn : ((if n = m then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = l then v else 1
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: refine' Or.inl ⟨rfl, not_ne_iff.mp fun hln => (hv _).elim⟩
state_before: case refine'_1.inl
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle k u * mulSingle n v
hk : ((if True then u else 1) * if k = l then v else 1) = (if k = k then u else 1) * if k = n then v else 1
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = k then u else 1) * if l = n then v else 1
hm : ((if True then u else 1) * if k = n then v else 1) = (if k = k then u else 1) * if k = l then v else 1
hn : ((if n = k then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = l then v else 1
⊢ k = k ∧ l = n ∨ u = v ∧ k = n ∧ l = k ∨ u * v = 1 ∧ k = l ∧ k = n

tactic: rcases eq_or_ne k l with (rfl | hkl)
state_before: case refine'_1.inl
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle k u * mulSingle n v
hk : ((if True then u else 1) * if k = l then v else 1) = (if k = k then u else 1) * if k = n then v else 1
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = k then u else 1) * if l = n then v else 1
hm : ((if True then u else 1) * if k = n then v else 1) = (if k = k then u else 1) * if k = l then v else 1
hn : ((if n = k then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = l then v else 1
hln : l ≠ n
⊢ v = 1

tactic: rwa [if_neg hln.symm, if_neg hln.symm, one_mul, one_mul] at hn
state_before: case refine'_1.inl.inl
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle k v = mulSingle k u * mulSingle n v
hk : ((if True then u else 1) * if k = k then v else 1) = (if k = k then u else 1) * if k = n then v else 1
hl : ((if k = k then u else 1) * if True then v else 1) = (if k = k then u else 1) * if k = n then v else 1
hm : ((if True then u else 1) * if k = n then v else 1) = (if k = k then u else 1) * if k = k then v else 1
hn : ((if n = k then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = k then v else 1
hln : k ≠ n
⊢ v = 1

tactic: rwa [if_neg hkl.symm, if_neg hln, one_mul, one_mul] at hl
state_before: case refine'_1.inl.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle k u * mulSingle n v
hk : ((if True then u else 1) * if k = l then v else 1) = (if k = k then u else 1) * if k = n then v else 1
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = k then u else 1) * if l = n then v else 1
hm : ((if True then u else 1) * if k = n then v else 1) = (if k = k then u else 1) * if k = l then v else 1
hn : ((if n = k then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = l then v else 1
hln : l ≠ n
hkl : k ≠ l
⊢ v = 1

tactic: rcases eq_or_ne m n with (rfl | hmn)
state_before: case refine'_1.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v
hk : ((if True then u else 1) * if k = l then v else 1) = (if k = m then u else 1) * if k = n then v else 1
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = m then u else 1) * if l = n then v else 1
hm : ((if True then u else 1) * if m = n then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hn : ((if n = m then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = l then v else 1
hkm : k ≠ m
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: rcases eq_or_ne k l with (rfl | hkl)
state_before: case refine'_1.inr.inl
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
hkm : k ≠ m
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle m v
hk : ((if True then u else 1) * if k = l then v else 1) = (if k = m then u else 1) * if k = m then v else 1
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = m then u else 1) * if l = m then v else 1
hm : ((if True then u else 1) * if m = m then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hn : ((if m = m then u else 1) * if True then v else 1) = (if m = k then u else 1) * if m = l then v else 1
⊢ k = m ∧ l = m ∨ u = v ∧ k = m ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = m

tactic: rw [if_neg hkm.symm, if_neg hkm.symm, one_mul, if_pos rfl] at hm
state_before: case refine'_1.inr.inl.inl
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k m : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
hkm : k ≠ m
h : mulSingle k u * mulSingle k v = mulSingle m u * mulSingle m v
hk : ((if True then u else 1) * if k = k then v else 1) = (if k = m then u else 1) * if k = m then v else 1
hl : ((if k = k then u else 1) * if True then v else 1) = (if k = m then u else 1) * if k = m then v else 1
hm : ((if True then u else 1) * if m = m then v else 1) = (if m = k then u else 1) * if m = k then v else 1
hn : ((if m = m then u else 1) * if True then v else 1) = (if m = k then u else 1) * if m = k then v else 1
⊢ k = m ∧ k = m ∨ u = v ∧ k = m ∧ k = m ∨ u * v = 1 ∧ k = k ∧ m = m

tactic: exact Or.inr (Or.inr ⟨hm, rfl, rfl⟩)
state_before: case refine'_1.inr.inl.inl
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k m : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
hkm : k ≠ m
h : mulSingle k u * mulSingle k v = mulSingle m u * mulSingle m v
hk : ((if True then u else 1) * if k = k then v else 1) = (if k = m then u else 1) * if k = m then v else 1
hl : ((if k = k then u else 1) * if True then v else 1) = (if k = m then u else 1) * if k = m then v else 1
hm : (if True then u else 1) * v = 1
hn : ((if m = m then u else 1) * if True then v else 1) = (if m = k then u else 1) * if m = k then v else 1
⊢ k = m ∧ k = m ∨ u = v ∧ k = m ∧ k = m ∨ u * v = 1 ∧ k = k ∧ m = m

tactic: simp only [if_neg hkm, if_neg hkl, mul_one] at hk
state_before: case refine'_1.inr.inl.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
hkm : k ≠ m
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle m v
hk : ((if True then u else 1) * if k = l then v else 1) = (if k = m then u else 1) * if k = m then v else 1
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = m then u else 1) * if l = m then v else 1
hm : ((if True then u else 1) * if m = m then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hn : ((if m = m then u else 1) * if True then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hkl : k ≠ l
⊢ k = m ∧ l = m ∨ u = v ∧ k = m ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = m

tactic: dsimp at hk
state_before: case refine'_1.inr.inl.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
hkm : k ≠ m
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle m v
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = m then u else 1) * if l = m then v else 1
hm : ((if True then u else 1) * if m = m then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hn : ((if m = m then u else 1) * if True then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hkl : k ≠ l
hk : (if True then u else 1) = 1
⊢ k = m ∧ l = m ∨ u = v ∧ k = m ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = m

tactic: contradiction
state_before: case refine'_1.inr.inl.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
hkm : k ≠ m
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle m v
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = m then u else 1) * if l = m then v else 1
hm : ((if True then u else 1) * if m = m then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hn : ((if m = m then u else 1) * if True then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hkl : k ≠ l
hk : u = 1
⊢ k = m ∧ l = m ∨ u = v ∧ k = m ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = m

tactic: rw [if_neg hkm.symm, if_neg hmn, one_mul, mul_one] at hm
state_before: case refine'_1.inr.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v
hk : ((if True then u else 1) * if k = l then v else 1) = (if k = m then u else 1) * if k = n then v else 1
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = m then u else 1) * if l = n then v else 1
hm : ((if True then u else 1) * if m = n then v else 1) = (if m = k then u else 1) * if m = l then v else 1
hn : ((if n = m then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = l then v else 1
hkm : k ≠ m
hmn : m ≠ n
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: obtain rfl := (ite_ne_right_iff.mp (ne_of_eq_of_ne hm.symm hu)).1
state_before: case refine'_1.inr.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v
hk : ((if True then u else 1) * if k = l then v else 1) = (if k = m then u else 1) * if k = n then v else 1
hl : ((if l = k then u else 1) * if True then v else 1) = (if l = m then u else 1) * if l = n then v else 1
hm : (if True then u else 1) = if m = l then v else 1
hn : ((if n = m then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = l then v else 1
hkm : k ≠ m
hmn : m ≠ n
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n

tactic: rw [if_neg hkm, if_neg hkm, one_mul, mul_one] at hk
state_before: case refine'_1.inr.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
hkm : k ≠ m
hmn : m ≠ n
h : mulSingle k u * mulSingle m v = mulSingle m u * mulSingle n v
hk : ((if True then u else 1) * if k = m then v else 1) = (if k = m then u else 1) * if k = n then v else 1
hl : ((if m = k then u else 1) * if True then v else 1) = (if m = m then u else 1) * if m = n then v else 1
hm : (if True then u else 1) = if m = m then v else 1
hn : ((if n = m then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = m then v else 1
⊢ k = m ∧ m = n ∨ u = v ∧ k = n ∧ m = m ∨ u * v = 1 ∧ k = m ∧ m = n

tactic: obtain rfl := (ite_ne_right_iff.mp (ne_of_eq_of_ne hk.symm hu)).1
state_before: case refine'_1.inr.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
hkm : k ≠ m
hmn : m ≠ n
h : mulSingle k u * mulSingle m v = mulSingle m u * mulSingle n v
hk : (if True then u else 1) = if k = n then v else 1
hl : ((if m = k then u else 1) * if True then v else 1) = (if m = m then u else 1) * if m = n then v else 1
hm : (if True then u else 1) = if m = m then v else 1
hn : ((if n = m then u else 1) * if True then v else 1) = (if n = k then u else 1) * if n = m then v else 1
⊢ k = m ∧ m = n ∨ u = v ∧ k = n ∧ m = m ∨ u * v = 1 ∧ k = m ∧ m = n

tactic: exact Or.inr (Or.inl ⟨hk.trans (if_pos rfl), rfl, rfl⟩)
state_before: case refine'_1.inr.inr
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k m : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
hkm : k ≠ m
hm : (if True then u else 1) = if m = m then v else 1
hmn : m ≠ k
h : mulSingle k u * mulSingle m v = mulSingle m u * mulSingle k v
hk : (if True then u else 1) = if k = k then v else 1
hl : ((if m = k then u else 1) * if True then v else 1) = (if m = m then u else 1) * if m = k then v else 1
hn : ((if k = m then u else 1) * if True then v else 1) = (if k = k then u else 1) * if k = m then v else 1
⊢ k = m ∧ m = k ∨ u = v ∧ k = k ∧ m = m ∨ u * v = 1 ∧ k = m ∧ m = k

tactic: rintro (⟨rfl, rfl⟩ | ⟨rfl, rfl, rfl⟩ | ⟨h, rfl, rfl⟩)
state_before: case refine'_2
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l m n : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
⊢ k = m ∧ l = n ∨ u = v ∧ k = n ∧ l = m ∨ u * v = 1 ∧ k = l ∧ m = n →
    mulSingle k u * mulSingle l v = mulSingle m u * mulSingle n v

tactic: rfl
state_before: case refine'_2.inl.intro
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
⊢ mulSingle k u * mulSingle l v = mulSingle k u * mulSingle l v

tactic: apply mul_comm
state_before: case refine'_2.inr.inl.intro.intro
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k l : I
u : M
hu hv : u ≠ 1
⊢ mulSingle k u * mulSingle l u = mulSingle l u * mulSingle k u

tactic: simp_rw [← Pi.mulSingle_mul, h, mulSingle_one]
state_before: case refine'_2.inr.inr.intro.intro
ι : Type ?u.81137
α : Type ?u.81140
I : Type u
f : I → Type v
x y : (i : I) → f i
i j : I
inst✝¹ : DecidableEq I
M : Type u_1
inst✝ : CommMonoid M
k m : I
u v : M
hu : u ≠ 1
hv : v ≠ 1
h : u * v = 1
⊢ mulSingle k u * mulSingle k v = mulSingle m u * mulSingle m v