proposition: Lemma proper_ring_rot r : proper_ring (rot n0 r) = proper_ring r.
proof: Proof. case lt2r: (2 < size r); first by rewrite !size_proper_ring ?size_rot. case: n0 r lt2r => [|[|i]] [|x [|y [|z r]]] //= _. by rewrite (canF_eq (plain_eq plainG)) eq_sym. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry patch sew snip color chromogram) fourcolor(coloring kempe)