∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} [inst : EquivBEq α] [inst_1 : LawfulHashable α] {l : List α} {k : α},
  Std.ExtDHashMap.Const.get? (Std.ExtDHashMap.Const.unitOfList l) k = if l.contains k = true then some () else none