def index(self, auth):
        if auth.getAbstract() is None:
            raise MaKaCError(_("cannot index an author of an abstract which is not included in a conference"))
        if auth.getAbstract().getOwner() != self._mgr:
            raise MaKaCError(_("cannot index an author of an abstract which does not belong to this conference"))
        key = self._getKey(auth)
        abstractId = str(auth.getAbstract().getId())
        if not self._idx.has_key(key):
            self._idx[key] = OIBTree.OIBTree()
        if not self._idx[key].has_key(abstractId):
            self._idx[key][abstractId] = 0
        self._idx[key][abstractId] += 1