def _dummy(name, token, expr, **kwargs):
    d = _dummy_(name, token, **kwargs)
    if d in expr.free_symbols:
        return Dummy(name, **kwargs)
    return d
Return a dummy. This will return the same dummy if the same token+name is
dataset/ETHPy150Open sympy/sympy/sympy/integrals/meijerint.py/_dummy