fact: Fixpoint gtree_table_sub (tab : gtree_table) n {struct tab} := match tab, n with | [::], _ => fun _ => GtreeEmpty | pt :: _, 0 => gtree_pair_sub pt | _ :: tab', n'.+1 => gtree_table_sub tab' n' end.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq) fourcolor(color chromogram gtree dyck)