Return GO IDs whose depth is 0 (BP, MF, CC) or depth is 1.

def get_gos_d0d1(self):
        """Return GO IDs whose depth is 0 (BP, MF, CC) or depth is 1."""
        return set([o.id for d in [0, 1] for o in self.gosubdag.rcntobj.depth2goobjs.get(d)])