unfold spminusf in |- *; auto.
Qed.

Theorem eqTerm_spminusf_com :
forall (a b c : Term A n) (nZc : ~ zeroP (A:=A) A0 eqA (n:=n) c)
(p q : list (Term A n)),
canonical A0 eqA ltM p ->
canonical A0 eqA ltM q ->
eqTerm (A:=A) eqA (n:=n) a b ->
divP A A0 eqA multA divA n a c ->
eqP A eqA n (spminusf a c nZc p q) (spminusf b c nZc p q).