include "lib.java.cd";
 package trees;

 Tree : Node | Leaf.
 Node = "(" <name> ident *s <children> List(Tree) ")".
 Leaf = <name> ident.

 Tuple = "<" *s <ns> List(ident) ">".
 Problem = "trees" *s <ts> List(Tree) *l
           "select" *s <ms> List(Tuple) EOF.