proposition: Lemma cnf_nat_sum0 x : cnfp x ->x +#f \0f = x.
proof: Proof. move => ox; symmetry; apply: (cnf_nat_sum_p3 ox cnfp0 ox) => e. by rewrite cnf_coef_or_e_zero (csum0r (CS_nat (NS_Vr e ox))). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)