∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} {β : Type v} {m : Std.DHashMap α fun x => β} [EquivBEq α]
  [LawfulHashable α] [inst : Inhabited β] {a : α}, Std.DHashMap.Const.get! m a = Std.DHashMap.Const.getD m a default