'Sequentially allocate values to localzeros.
When a value is identified as being more extreme than another member it
replaces that member; if this is never true, then the value is simply
appended to the localzeros.'

@classmethod
def _find_localzeros(cls, values, **options):

    localzeros = set()
    for v in values:
        is_newzero = True
        localzeros_ = list(localzeros)
        for z in localzeros_:
            if (id(v) == id(z)):
                is_newzero = False
            else:
                con = cls._is_connected(v, z)
                if con:
                    is_newzero = False
                    if ((con is True) or (con == cls)):
                        localzeros.remove(z)
                        localzeros.update([v])
        if is_newzero:
            localzeros.update([v])
    return localzeros
