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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _contained_parameters(expression):
 """ Determine which parameters are contained in this expression. :param Expression expression: expression involving parameters :return: set of parameters contained in this expression :rtype: set """

    if isinstance(expression, BinaryExp):
        return _contained_parameters(expression.op1) | _contained_parameters(expression.op2)
    elif isinstance(expression, Function):
        return _contained_parameters(expression.expression)
    elif isinstance(expression, Parameter):
        return {expression}
    else:
        return set()