∀ {α : Type u} {m : Std.HashSet.Raw α} [inst : BEq α] [inst_1 : Hashable α] [inst_2 : EquivBEq α]
  [inst_3 : LawfulHashable α] (h : m.WF) {k : α} {h' : (m.get? k).isSome = true}, (m.get? k).get h' = m.get k ⋯