Theorem: Tutorial.mul_inv_rev (Tutorial/Advanced/Algebra/Lecture1.lean)

State before:
A : Type ?u.3654
G : Type
inst✝¹ : Ring A
inst✝ : Group G
a b : G
⊢ (a * b)⁻¹ = b⁻¹ * a⁻¹
Tactic:
sorry
State after:
no goals