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

State before:
G : Type
inst✝ : Group₁ G
a : G
⊢ a ⋄ a⁻¹ = 𝟙
Tactic:
rw [← inv_dia a⁻¹, inv_eq_of_dia (inv_dia a)]
State after:
no goals