fact: Definition add p1 p2 := let: Gpoint x1 y1 := p1 in let: Gpoint x2 y2 := p2 in Gpoint (x1 + x2) (y1 + y2).
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)