583.lean:31:8: error: 1 unsolved subgoal
A : Type,
B : Type,
s1 : group A,
s2 : group B,
f : A → B,
Hom : is_hom f,
a : A,
P : f a⁻¹ * f a = 1
⊢ f a⁻¹ = (f a)⁻¹
583.lean:27:8: error: failed to add declaration 'group_hom.hom_map_inv' to environment, value has metavariables
remark: set 'formatter.hide_full_terms' to false to see the complete term
  λ (A : Type) (B : Type) (s1 : …) (s2 : …) (f : …) (Hom : …) (a : A),
    have P [visible] : …, from …,
    ?M_1