def get_nfa(self, idgenerator):
left = self.childs[0]
right = self.childs[1]
left_nfa = left.get_nfa(idgenerator)
right_nfa = right.get_nfa(idgenerator)
start, accept = idgenerator.nextID(), idgenerator.nextID()
root_nfa = NFA().startState(start).acceptState(accept)
root_nfa.append([left_nfa, right_nfa])
for sub_nfa in [left_nfa, right_nfa]:
root_nfa.addTransitions(start, EPSILON, sub_nfa.start)
root_nfa.addTransitions(sub_nfa.accept, EPSILON, accept)
return root_nfa
