{Checkpoint, 0, 0},
		{SetEqual, 2, 100},
		{Ordered, 1, 107},
		{Ordered, 100, 6},

		// SetEqual with new node
		{Undo, 0, 0},
		{Checkpoint, 0, 0},
		{SetEqual, 2, 400},
		{SetEqual, 401, 2},
		{Equal, 400, 401},
		{Ordered, 1, 400},
		{Ordered, 400, 6},
		{Ordered, 1, 401},
		{Ordered, 401, 6},
		{Ordered_Fail, 2, 401},

		// SetEqual unseen nodes and then connect

		panic("should not call SetOrder with n1==n2")
	}
	return po.setOrder(n1, n2, false)
}

// SetEqual records that n1==n2. Returns false if this is a contradiction
// (that is, if it is already recorded that n1<n2 or n2<n1).
// Complexity is O(1) if n2 was never seen before, or O(n) otherwise.
func (po *poset) SetEqual(n1, n2 *Value) bool {
	if debugPoset {
		defer po.CheckIntegrity()
	}
	if n1.ID == n2.ID {