fact: Definition sew_node (w : sew_dart) : sew_dart := match w with | existT SewDisk xd => sewd (node xd) | existT SewRest ur => sewr (node (sval ur)) end.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color patch)