fact: Definition cap_interval (xz1 xz2 : interval) := let: Interval x1 z1 := xz1 in let: Interval x2 z2 := xz2 in Interval (max x1 x2) (min z1 z2).
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype tuple path fingraph bigop order ssralg) mathcomp(ssrnum ssrint div intdiv) fourcolor(hypermap geometry coloring grid matte) fourcolor(real realplane) Coq(Setoid Morphisms) fourcolor(realsyntax realprop)