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

State before:
A : Type ?u.4111
G : Type
inst✝¹ : Ring A
inst✝ : Group G
a b : G
⊢ a⁻¹ * b = 1 ↔ a = b
Tactic:
sorry
State after:
no goals