def METHOD_NAME(ntuple1, ntuple2, selector2=None):
    # assume the two ntuples have the very same tracks except possibly
    # for their parameters
    h1 = makeHistos()
    h2 = makeHistos()
    for (event1, event2) in itertools.izip(ntuple1, ntuple2):
        #print event1.eventIdStr(), event2.eventIdStr()
        if event1.eventId() != event2.eventId():
            raise Exception("Inconsistent events %s != %s" % (event1.eventIdStr(), event2.eventIdStr()))
        for (track1, track2) in itertools.izip(event1.tracks(), event2.tracks()):
            if selector2 is not None and not selector2(track2):
                continue
            fillHistos(h1, track1)
            fillHistos(h2, track2)
    return (h1, h2)