Theorem: Group₃.mul_inv (LeanCourse/MIL/C07_Hierarchies/solutions/Solutions_S01_Basics.lean)

State before:
G : Type
inst✝ : Group₃ G
a : G
⊢ a * a⁻¹ = 1
Tactic:
rw [← inv_mul a⁻¹, inv_eq_of_mul (inv_mul a)]
State after:
no goals