proposition: Lemma codom_snipr : codom snipr =i [predC diskE].
proof: Proof. move=> z; apply/imageP/idP => [[[y dE'y] _ /= -> //] | dE'z]. by exists (sub z dE'z). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap jordan color geometry patch)