'Rename all occurrences of the variable introduced by this variable
binder in the expression to ``newvar``.
:param newvar: ``Variable``, for the new variable'

def alpha_convert(self, newvar):

    assert isinstance(newvar, Variable), (u'%s    is    not    a    Variable' % newvar)
    return self.__class__(newvar, self.term.replace(self.variable, VariableExpression(newvar), True))
