∀ {α : Type u} {m : Std.HashSet.Raw α} [inst : BEq α] [inst_1 : Hashable α] [EquivBEq α] [LawfulHashable α]
  [inst_4 : Inhabited α], m.WF → ∀ {a : α}, m.contains a = true → m.get? a = some (m.get! a)