Instance mkPinj_ext : Proper (eq ==> Pequiv ==> Pequiv) mkPinj.

(* Specifications: *)
Lemma pow_pos_add x i j : x^(j + i) == x^i * x^j.
Lemma ceqb_spec c c' : BoolSpec ([c] == [c']) True (c ?=! c').
Lemma mkPX_ok l P i Q : (mkPX P i Q)@l == P@l * (hd l)^i + Q@(tail l).