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

State before:
A : Type ?u.2445
G : Type
inst✝¹ : Ring A
inst✝ : Group G
a b : G
⊢ a * (a⁻¹ * b) = b
Tactic:
rw [← mul_assoc]
State after:
A : Type ?u.2445
G : Type
inst✝¹ : Ring A
inst✝ : Group G
a b : G
⊢ a * a⁻¹ * b = b

State before:
A : Type ?u.2445
G : Type
inst✝¹ : Ring A
inst✝ : Group G
a b : G
⊢ a * a⁻¹ * b = b
Tactic:
sorry
State after:
no goals