<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def dist(self, x1, x2):
 """Return the distance between ``x1`` and ``x2``. Parameters x1, x2 : `LinearSpaceElement` Elements whose distance to compute. Returns ------- dist : float Distance between ``x1`` and ``x2``. """

        if x1 not in self:
            raise LinearSpaceTypeError('`x1` {!r} is not an element of '
                                       '{!r}'.format(x1, self))
        if x2 not in self:
            raise LinearSpaceTypeError('`x2` {!r} is not an element of '
                                       '{!r}'.format(x2, self))
        return float(self._dist(x1, x2))