fact: Fixpoint Tree_to_tree e:= match e with | Tbase n => J \0c (nat_to_B n) | Tpowerset e' => J \1c (Tree_to_tree e') | Tproduct e' e'' => J \2c (J (Tree_to_tree e') (Tree_to_tree e'')) end.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq)