∀ {α : Type u} {β : Type v} [inst : BEq α] (a : α) (x : Std.DHashMap.Internal.AssocList α fun x => β),
  Std.DHashMap.Internal.AssocList.get? a x =
    match x with
    | Std.DHashMap.Internal.AssocList.nil => none
    | Std.DHashMap.Internal.AssocList.cons k v es =>
      bif k == a then some v else Std.DHashMap.Internal.AssocList.get? a es