code: def test_complex(self):
      grammar = nltk.data.load("grammars/large_grammars/atis.cfg")
      self.assertFalse(grammar.is_flexible_chomsky_normal_form())
      self.assertFalse(grammar.is_chomsky_normal_form())
      grammar = grammar.chomsky_normal_form(flexible=True)
      self.assertTrue(grammar.is_flexible_chomsky_normal_form())
      self.assertFalse(grammar.is_chomsky_normal_form())
  
imports: import unittest
  import nltk
  from nltk.grammar import CFG
label_desc: Use image node_id 2 for calling the ChomskyNormalFormForCFGTest obj's underlying member method code with example usage: obj.test_complex() without return types