def METHOD_NAME(self):
    """
    Create a new evolver for this pset. For a discussion on evolvers in general see the
    documentation for the pvector evolver.
    Create the evolver and perform various mutating updates to it:
    >>> s1 = s(1, 2, 3)
    >>> e = s1.evolver()
    >>> _ = e.add(4)
    >>> len(e)
    4
    >>> _ = e.remove(1)
    The underlying pset remains the same:
    >>> s1
    pset([1, 2, 3])
    The changes are kept in the evolver. An updated pmap can be created using the
    persistent() function on the evolver.
    >>> s2 = e.persistent()
    >>> s2
    pset([2, 3, 4])
    The new pset will share data with the original pset in the same way that would have
    been done if only using operations on the pset.
    """
    return PSet._Evolver(self)