∀ {α : Type u} {β : α → Type v} {x : BEq α} {x_1 : Hashable α} [inst : LawfulBEq α] {l : List ((a : α) × β a)} {k : α},
  (List.map Sigma.fst l).contains k = false → (Std.DHashMap.ofList l).get? k = none