Definition invTerm : Term -> Term.

(* Specifications: *)
Theorem plusTerm_invTerm_zeroP : forall a : Term, zeroP (plusTerm a (invTerm a)).
Theorem zeroP_invTerm_zeroP : forall a : Term, zeroP a -> zeroP (invTerm a).
Theorem invTerm_invol : forall a : Term, eqTerm a (invTerm (invTerm a)).
Theorem nZero_invTerm_nZero : forall a : Term, ~ zeroP a -> ~ zeroP (invTerm a).