apply inv_one_eq_one
α : Type u_1
G : group α
H : Set α := trivial_subgroup G
hH : H = trivial_subgroup G
hmul_mem : ∀ (a b : α), a ∈ H → b ∈ H → a * b ∈ H
hone_mem : has_one.one ∈ H
a : α
ha : a = has_one.one
⊢ group.inv has_one.one ∈ H
no goals