class_docstr: A list of sets of Variables.
class_docstr_tok: ["A","list","of","sets","of","Variables","."]
docstr: :param item: ``Variable``
  :return: the set containing 'item'
docstr_tok: [":","param","item",":","``","Variable","``",":","return",":","the","set","containing","'item","'"]
code: def __getitem__(self, item):
      """
      :param item: ``Variable``
      :return: the set containing 'item'
      """
      assert isinstance(item, Variable)
      for s in self:
          if item in s:
              return s
      # item is not found in any existing set.  so create a new set
      new = {item}
      self.append(new)
      return new
  
imports: from collections import defaultdict
  from functools import reduce
  from nltk.inference.api import Prover, ProverCommandDecorator
  from nltk.inference.prover9 import Prover9, Prover9Command
  from nltk.sem.logic import AbstractVariableExpression, AllExpression, AndExpression, ApplicationExpression, BooleanExpression, EqualityExpression, ExistsExpression, Expression, ImpExpression, NegatedExpression, Variable, VariableExpression, operator, unique_variable
label_desc: Use image node_id 1 for calling the SetHolder obj's underlying member method code with example usage: obj.__getitem__(item) and returns: new, s