proposition: Theorem eqptail_spminusf_com : forall (a b : Term A n) (nZb : ~ zeroP (A:=A) A0 eqA (n:=n) b) (p q r : list (Term A n)), canonical A0 eqA ltM p -> canonical A0 eqA ltM q -> canonical A0 eqA ltM r -> eqP A eqA n p q -> divP A A0 eqA multA divA n a b -> eqP A eqA n (spminusf a b nZb p r) (spminusf a b nZb q r).
proof: Proof. Proof using plusA os cs. unfold spminusf in |- *; auto. Qed.