po.noneq[i1] = bs
	} else if bs.Test(i2) {
		// Already recorded
		return
	}
	bs.Set(i2)
	po.upushneq(i1, i2)
}

// CheckIntegrity verifies internal integrity of a poset. It is intended
// for debugging purposes.
func (po *poset) CheckIntegrity() {
	// Record which index is a constant
	constants := newBitset(int(po.lastidx + 1))
	for _, c := range po.constants {
		constants.Set(c)
	}

			t.Log("Undo stack", po.undo)
			po.Undo()
		default:
			panic("unimplemented")
		}

		if false {
			po.DotDump(fmt.Sprintf("op%d.dot", idx), fmt.Sprintf("Last op: %v", op))
		}

		po.CheckIntegrity()
	}

	// Check that the poset is completely empty
	if err := po.CheckEmpty(); err != nil {
		t.Error(err)
	}
}

func TestPoset(t *testing.T) {
	testPosetOps(t, false, []posetTestOp{