code: def _collect_variable_renaming(
              cls, expression: Expression, position: List[int]=None, variables: Dict[str, str]=None
      ) -> Dict[str, str]:
          
          if position is None:
              position = [0]
          if variables is None:
              variables = {}
          if getattr(expression, 'variable_name', False):
              if expression.variable_name not in variables:
                  variables[expression.variable_name] = cls._get_name_for_position(position, variables.values())
          position[-1] += 1
          if isinstance(expression, Operation):
              if isinstance(expression, CommutativeOperation):
                  for operand in op_iter(expression):
                      position.append(0)
                      cls._collect_variable_renaming(operand, position, variables)
                      position.pop()
              else:
                  for operand in op_iter(expression):
                      cls._collect_variable_renaming(operand, position, variables)
  
          return variables
docs: Return renaming for the variables in the expression.
  
          The variable names are generated according to the position of the variable in the expression. The goal is to
          rename variables in structurally identical patterns so that the automaton contains less redundant states.