simp
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
⊢ { mem := fun x s => Set.isMember x }.1 has_one.one H
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
⊢ Set.isMember has_one.one