∀ {α : Type u} {β : Type v} {x : BEq α} {x_1 : Hashable α} {m : Std.HashMap α β} [EquivBEq α] [LawfulHashable α]
  {l : List (α × β)} {k : α}, (m.insertMany l).contains k = (m.contains k || (List.map Prod.fst l).contains k)