Definition inv : list (Term A n) -> Term A n -> Term A n.

Theorem pluspf_is_minuspf : forall p q : list (Term A n), canonical A0 eqA ltM p -> canonical A0 eqA ltM q -> eqP A eqA n (pluspf (A:=A) A0 (eqA:=eqA) plusA eqA_dec (n:=n) (ltM:=ltM) ltM_dec p q) (minuspf p (mults (A:=A) multA (n:=n) (invTerm (A:=A) invA (n:=n) (T1 A1 n)) q)).