∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} {β : Type v} {m : Std.ExtDHashMap α fun x => β} [inst : EquivBEq α]
  [inst_1 : LawfulHashable α] {l : List (α × β)} {k : α},
  (List.map Prod.fst l).contains k = false →
    Std.ExtDHashMap.Const.get? (Std.ExtDHashMap.Const.insertMany m l) k = Std.ExtDHashMap.Const.get? m k