code: def penn_to_wn(tag):
      
      if tag.startswith('N'):
          return 'n'
  
      if tag.startswith('V'):
          return 'v'
  
      if tag.startswith('J'):
          return 'a'
  
      if tag.startswith('R'):
          return 'r'
  
      return None
docs: Convert between a Penn Treebank tag to a simplified Wordnet tag