disappear element in python

Question

classes = [[\'A\', \'B\', \'C\', \'D\', \'G\', \'H\'], [\'B\', \'C\', \'E\', \'G\', \'H\', \'K\', \'L\'], [\'C\', \'E\', \'D\', \'H\', \'K\', \'L\'], [\'E\', \'D\', \'F\