(* Finally, we must show that f_Sn preserves unsquashing. *)

Lemma fSn_unsquash : forall k1,
level k1 <= n + 1 ->
forall U1,
U1 = K1.unsquash k1 ->
K2.unsquash (f_Sn k1) = (fst U1, f_F' (g_Sn) (snd U1)).