(*** max_SS *)
lemma nmax_succ_bi (n1) (n2): ↑(n1 ∨ n2) = (↑n1 ∨ ↑n2).
#n1 #n2
-@trans_eq [3: @ntri_succ_bi | skip ] (**) (* rewrite fails because δ-expansion gets in the way *)
+@trans_eq [3: @ntri_succ_bi | skip ] (* * rewrite fails because δ-expansion gets in the way *)
<ntri_f_tri //
qed.