Theorem: Tutorial.inv_inv (Solution/Advanced/Algebra/Lecture1.lean)

State before:
A : Type ?u.18884
G : Type
inst✝¹ : Ring A
inst✝ : Group G
a : G
⊢ a⁻¹⁻¹ = a
Tactic:
apply inv_eq_of_mul_eq_one_left
State after:
case a
A : Type ?u.18884
G : Type
inst✝¹ : Ring A
inst✝ : Group G
a : G
⊢ a * a⁻¹ = 1

State before:
case a
A : Type ?u.18884
G : Type
inst✝¹ : Ring A
inst✝ : Group G
a : G
⊢ a * a⁻¹ = 1
Tactic:
simp
State after:
no goals