proposition: Lemma orsum_invariant4 r1 r2 r3 r4: r1 \Is r3 -> r2 \Is r4 -> (order_sum2 r1 r2) \Is (order_sum2 r3 r4).
proof: Proof. move=> h1 h2; rewrite /order_sum2. move: cdo_wor => [[res _] sr]. apply: orsum_invariant2; rewrite ?sr;aww. by move=> i itp; try_lvariant itp. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)