+ else if ("grammar".equals(head)) { for(Tree<String> t : tree.children()) walk(t); return this; }
+ else if ("*".equals(head)) return Repeat.many0((Element)walk(tree.child(0)));
+ else if ("+".equals(head)) return Repeat.many1((Element)walk(tree.child(0)));
+ else if ("+/".equals(head)) return Repeat.many1((Element)walk(tree.child(0)), (Element)walk(tree.child(1)));
+ else if ("*/".equals(head)) return Repeat.many0((Element)walk(tree.child(0)), (Element)walk(tree.child(1)));
+ else if ("**".equals(head)) return Repeat.maximal(Repeat.many0((Element)walk(tree.child(0))));
+ else if ("++".equals(head)) return Repeat.maximal(Repeat.many1((Element)walk(tree.child(0))));
+ else if ("?".equals(head)) return Repeat.maybe((Element)walk(tree.child(0)));
+ else if ("&".equals(head)) return ((PreSequence)walk(tree,0)).and(new PreSequence((Element[])Reflection.lub((Object[])walk(tree, 1)), null).buildSequence(null, true, false));
+ else if ("&~".equals(head)) return ((PreSequence)walk(tree,0)).not(new PreSequence((Element[])Reflection.lub((Object[])walk(tree, 1)), null).buildSequence(null, true, false));
+ else if ("epsilon".equals(head)) return Union.epsilon;
+ else if ("()".equals(head)) return Union.epsilon;
+ else if (")".equals(head)) return SELF;
+ else if ("nonTerminal".equals(head)) return nonTerminal(string(tree.child(0)), null, false, false);
+ else if ("::=".equals(head)) return nonTerminal(string(tree.child(0)), (PreSequence[][])walk(tree, 1), false, false);
+ else if ("!::=".equals(head)) return nonTerminal(string(tree.child(0)), (PreSequence[][])walk(tree, 1), false, true);
+ else if ("(".equals(head)) return nonTerminal("anon"+(anon++), (PreSequence[][])walk(tree, 0), false, false);