proposition: Lemma pmap_subcoloring n k : subcoloring k -> subcoloring (pmap n k).
proof: Proof. case=> kP adj'k /(size_pmap n kP)-le_kn_nc; have knP := pmap_plain n kP. by split=> // z1 z2 /adj'k-not_kz12 /pmap_sub. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(path ssralg ssrint) fourcolor(real realplane realsyntax realprop) fourcolor(grid approx)