proposition: Lemma nds_tn_zero: nds_tn_sup \0c = \1c.
proof: Proof. move:(nds_tn_def NS0) => [_ _ [X ax <-] _]. rewrite /nds_tn_C /nds_tn_S setP_0 setUf_1 cardinal_set0 permutations_set0. by rewrite funI_set1 cardinal_set1. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)