sig
type t
type 'a embedding
val embed : unit -> 'a BottomUp.Univ.embedding
val pack : 'a BottomUp.Univ.embedding -> 'a -> BottomUp.Univ.t
val unpack : 'a BottomUp.Univ.embedding -> BottomUp.Univ.t -> 'a option
val compatible : 'a BottomUp.Univ.embedding -> BottomUp.Univ.t -> bool
end