':param variable: ``Variable``, for the variable
:param term: ``Expression``, for the term'

def __init__(self, variable, term):

    assert isinstance(variable, Variable), (u'%s    is    not    a    Variable' % variable)
    assert isinstance(term, Expression), (u'%s    is    not    an    Expression' % term)
    self.variable = variable
    self.term = term
