∀ {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] [inst_2 : Inhabited β] {a : α},
  Std.ExtDHashMap.Const.get! m a = Std.ExtDHashMap.Const.getD m a default