proposition: Lemma not_g4: ~(gorgeous 4).
proof: Proof. case=>//n Ih /eqP; last by rewrite addnC eqSS. case: n Ih=>//n Ih. rewrite addnC !eqSS. move/eqP=>Z; subst n. by apply:not_g1. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq)