'Return a list of the dummy variables
>>> from sympy import Sum
>>> from sympy.abc import x, i
>>> Sum(x**i, (i, 1, 3)).variables
[i]
See Also
function, limits, free_symbols
as_dummy : Rename dummy variables
transform : Perform mapping on the dummy variable'

@property
def variables(self):

    return [l[0] for l in self.limits]
