private static <L> void appendPreTerminalYield(Tree<L> tree, List<L> yield) {
if (tree.isPreTerminal()) {
yield.add(tree.getLabel());
return;
}
for (Tree<L> child : tree.getChildren()) {
appendPreTerminalYield(child, yield);
}
}
public List<L> getPreTerminalYield() {
List<L> yield = new ArrayList<L>();
appendPreTerminalYield(this, yield);
return yield;
}