Theorem: Permutation.eq_inv_of_mul_eq_left (Fifteen/Data/Permutation/Basic.lean)

State before:
n : Nat
x y : Permutation n
h : x * y = 1
this : (fun x_1 => inv x * x_1) (x * y) = (fun x_1 => inv x * x_1) 1
⊢ y = inv x
Tactic:
conv at this =>
  dsimp; rewrite [← mul_assoc, inv_mul, one_mul, mul_one]
State after:
n : Nat
x y : Permutation n
h : x * y = 1
this : y = inv x
⊢ y = inv x

State before:
n : Nat
x y : Permutation n
h : x * y = 1
this : y = inv x
⊢ y = inv x
Tactic:
exact this
State after:
no goals