'Pop a nonterminal.  (Internal)'

def pop(self):

    (popdfa, popstate, popnode) = self.stack.pop()
    newnode = self.convert(self.grammar, popnode)
    if (newnode is not None):
        if self.stack:
            (dfa, state, node) = self.stack[(-1)]
            node[(-1)].append(newnode)
        else:
            self.rootnode = newnode
            self.rootnode.used_names = self.used_names
    return
