diff --git a/lang/gg/gg.go b/lang/gg/gg.go
index 7cc4edd..0a6ccd8 100644
--- a/lang/gg/gg.go
+++ b/lang/gg/gg.go
@@ -8,6 +8,8 @@ import (
 	"hash"
 )
 
+// TODO rename half-edge to open-edge
+
 // Identifier is implemented by any value which can return a unique string for
 // itself via an Identify method
 type Identifier interface {
@@ -121,6 +123,18 @@ func (v vertex) hasHalfEdge(he HalfEdge) bool {
 	return false
 }
 
+func (v vertex) cpAndDelHalfEdge(he HalfEdge) (vertex, bool) {
+	heID := identify(he)
+	for i, in := range v.in {
+		if identify(in) == heID {
+			v = v.cp()
+			v.in = append(v.in[:i], v.in[i+1:]...)
+			return v, true
+		}
+	}
+	return v, false
+}
+
 // Graph is a wrapper around a set of connected Vertices
 type Graph struct {
 	vM   map[string]vertex // only contains value vertices
@@ -182,11 +196,11 @@ func JunctionOut(in []HalfEdge, edgeVal Identifier) HalfEdge {
 	}
 }
 
-// ValueIn takes a HalfEdge and connects it to the Value Vertex containing val,
-// and returns the new Graph which reflects that connection. Any Vertices
+// AddValueIn takes a HalfEdge and connects it to the Value Vertex containing
+// val, returning the new Graph which reflects that connection. Any Vertices
 // referenced within the HalfEdge which do not yet exist in the Graph will also
 // be created in this step.
-func (g *Graph) ValueIn(he HalfEdge, val Identifier) *Graph {
+func (g *Graph) AddValueIn(he HalfEdge, val Identifier) *Graph {
 	to := vertex{
 		VertexType: Value,
 		val:        val,
@@ -217,18 +231,121 @@ func (g *Graph) ValueIn(he HalfEdge, val Identifier) *Graph {
 			if _, ok := g.vM[vID]; !ok {
 				g.vM[vID] = v
 			}
-		}
-		for _, e := range v.in {
-			persist(e.fromV)
+		} else {
+			for _, e := range v.in {
+				persist(e.fromV)
+			}
 		}
 	}
 	delete(g.vM, toID)
 	persist(to)
+	for _, e := range to.in {
+		persist(e.fromV)
+	}
 
 	return g
 }
 
-// TODO Merge
+// DelValueIn takes a HalfEdge and disconnects it from the Value Vertex
+// containing val, returning the new Graph which reflects the disconnection. If
+// the Value Vertex doesn't exist within the graph, or it doesn't have the given
+// HalfEdge, no changes are made. Any vertices referenced by the HalfEdge for
+// which that edge is their only outgoing edge will be removed from the Graph.
+func (g *Graph) DelValueIn(he HalfEdge, val Identifier) *Graph {
+	to := vertex{
+		VertexType: Value,
+		val:        val,
+	}
+	toID := identify(to)
+
+	// pull to out of the graph. if it's not there then bail
+	var ok bool
+	if to, ok = g.vM[toID]; !ok {
+		return g
+	}
+
+	// get new copy of to without the half-edge, or return if the half-edge
+	// wasn't even in to
+	to, ok = to.cpAndDelHalfEdge(he)
+	if !ok {
+		return g
+	}
+	g = g.cp()
+	g.vM[toID] = to
+
+	// connectedTo returns whether the vertex has any connections with the
+	// vertex of the given id, descending recursively
+	var connectedTo func(string, vertex) bool
+	connectedTo = func(vID string, curr vertex) bool {
+		for _, in := range curr.in {
+			if in.fromV.VertexType == Value && identify(in.fromV) == vID {
+				return true
+			} else if in.fromV.VertexType == Junction && connectedTo(vID, in.fromV) {
+				return true
+			}
+		}
+		return false
+	}
+
+	// isOrphaned returns whether the given vertex has any connections to other
+	// nodes in the graph
+	isOrphaned := func(v vertex) bool {
+		vID := identify(v)
+		if v, ok := g.vM[vID]; ok && len(v.in) > 0 {
+			return false
+		}
+		for vID2, v2 := range g.vM {
+			if vID2 == vID {
+				continue
+			} else if connectedTo(vID, v2) {
+				return false
+			}
+		}
+		return true
+	}
+
+	// if to is orphaned get rid of it
+	if isOrphaned(to) {
+		delete(g.vM, toID)
+	}
+
+	// rmOrphaned descends down the given HalfEdge and removes any Value
+	// Vertices referenced in it which are now orphaned
+	var rmOrphaned func(HalfEdge)
+	rmOrphaned = func(he HalfEdge) {
+		if he.fromV.VertexType == Value && isOrphaned(he.fromV) {
+			delete(g.vM, identify(he.fromV))
+		} else if he.fromV.VertexType == Junction {
+			for _, juncHe := range he.fromV.in {
+				rmOrphaned(juncHe)
+			}
+		}
+	}
+	rmOrphaned(he)
+
+	return g
+}
+
+// Union takes in another Graph and returns a new one which is the union of the
+// two. Value vertices which are shared between the two will be merged so that
+// the new vertex has the input edges of both.
+func (g *Graph) Union(g2 *Graph) *Graph {
+	g = g.cp()
+	for vID, v2 := range g2.vM {
+		v, ok := g.vM[vID]
+		if !ok {
+			v = v2
+		} else {
+			for _, v2e := range v2.in {
+				if !v.hasHalfEdge(v2e) {
+					v.in = append(v.in, v2e)
+				}
+			}
+		}
+		g.vM[vID] = v
+	}
+	return g
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 // Graph traversal
@@ -287,6 +404,16 @@ func (g *Graph) Value(val Identifier) *Vertex {
 	return g.view[identify(val)]
 }
 
+// Values returns all Value Vertices in the Graph
+func (g *Graph) Values() []*Vertex {
+	g.makeView()
+	vv := make([]*Vertex, 0, len(g.view))
+	for _, v := range g.view {
+		vv = append(vv, v)
+	}
+	return vv
+}
+
 // Equal returns whether or not the two Graphs are equivalent in value
 func Equal(g1, g2 *Graph) bool {
 	if len(g1.vM) != len(g2.vM) {
diff --git a/lang/gg/gg_test.go b/lang/gg/gg_test.go
index 668e11b..9f8a51d 100644
--- a/lang/gg/gg_test.go
+++ b/lang/gg/gg_test.go
@@ -83,7 +83,7 @@ func TestGraph(t *T) {
 		mkTest(
 			"values-basic",
 			func() *Graph {
-				return Null.ValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+				return Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
 			},
 			value("v0"),
 			value("v1", edge("e0", value("v0"))),
@@ -92,8 +92,8 @@ func TestGraph(t *T) {
 		mkTest(
 			"values-2edges",
 			func() *Graph {
-				g0 := Null.ValueIn(ValueOut(id("v0"), id("e0")), id("v2"))
-				return g0.ValueIn(ValueOut(id("v1"), id("e1")), id("v2"))
+				g0 := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v2"))
+				return g0.AddValueIn(ValueOut(id("v1"), id("e1")), id("v2"))
 			},
 			value("v0"),
 			value("v1"),
@@ -106,8 +106,8 @@ func TestGraph(t *T) {
 		mkTest(
 			"values-separate",
 			func() *Graph {
-				g0 := Null.ValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
-				return g0.ValueIn(ValueOut(id("v2"), id("e2")), id("v3"))
+				g0 := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+				return g0.AddValueIn(ValueOut(id("v2"), id("e2")), id("v3"))
 			},
 			value("v0"),
 			value("v1", edge("e0", value("v0"))),
@@ -118,7 +118,7 @@ func TestGraph(t *T) {
 		mkTest(
 			"values-circular",
 			func() *Graph {
-				return Null.ValueIn(ValueOut(id("v0"), id("e")), id("v0"))
+				return Null.AddValueIn(ValueOut(id("v0"), id("e")), id("v0"))
 			},
 			value("v0", edge("e", value("v0"))),
 		),
@@ -126,8 +126,8 @@ func TestGraph(t *T) {
 		mkTest(
 			"values-circular2",
 			func() *Graph {
-				g0 := Null.ValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
-				return g0.ValueIn(ValueOut(id("v1"), id("e1")), id("v0"))
+				g0 := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+				return g0.AddValueIn(ValueOut(id("v1"), id("e1")), id("v0"))
 			},
 			value("v0", edge("e1", value("v1", edge("e0", value("v0"))))),
 			value("v1", edge("e0", value("v0", edge("e1", value("v1"))))),
@@ -136,9 +136,9 @@ func TestGraph(t *T) {
 		mkTest(
 			"values-circular3",
 			func() *Graph {
-				g0 := Null.ValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
-				g1 := g0.ValueIn(ValueOut(id("v1"), id("e1")), id("v2"))
-				return g1.ValueIn(ValueOut(id("v2"), id("e2")), id("v1"))
+				g0 := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+				g1 := g0.AddValueIn(ValueOut(id("v1"), id("e1")), id("v2"))
+				return g1.AddValueIn(ValueOut(id("v2"), id("e2")), id("v1"))
 			},
 			value("v0"),
 			value("v1",
@@ -157,7 +157,7 @@ func TestGraph(t *T) {
 				e0 := ValueOut(id("v0"), id("e0"))
 				e1 := ValueOut(id("v1"), id("e1"))
 				ej0 := JunctionOut([]HalfEdge{e0, e1}, id("ej0"))
-				return Null.ValueIn(ej0, id("v2"))
+				return Null.AddValueIn(ej0, id("v2"))
 			},
 			value("v0"), value("v1"),
 			value("v2", junction("ej0",
@@ -176,7 +176,7 @@ func TestGraph(t *T) {
 				e11 := ValueOut(id("v1"), id("e11"))
 				ej1 := JunctionOut([]HalfEdge{e01, e11}, id("ej1"))
 				ej2 := JunctionOut([]HalfEdge{ej0, ej1}, id("ej2"))
-				return Null.ValueIn(ej2, id("v2"))
+				return Null.AddValueIn(ej2, id("v2"))
 			},
 			value("v0"), value("v1"),
 			value("v2", junction("ej2",
@@ -197,11 +197,11 @@ func TestGraph(t *T) {
 				e0 := ValueOut(id("v0"), id("e0"))
 				e1 := ValueOut(id("v1"), id("e1"))
 				ej0 := JunctionOut([]HalfEdge{e0, e1}, id("ej0"))
-				g0 := Null.ValueIn(ej0, id("v2"))
+				g0 := Null.AddValueIn(ej0, id("v2"))
 				e20 := ValueOut(id("v2"), id("e20"))
-				g1 := g0.ValueIn(e20, id("v0"))
+				g1 := g0.AddValueIn(e20, id("v0"))
 				e21 := ValueOut(id("v2"), id("e21"))
-				return g1.ValueIn(e21, id("v1"))
+				return g1.AddValueIn(e21, id("v1"))
 			},
 			value("v0", edge("e20", value("v2", junction("ej0",
 				edge("e0", value("v0")),
@@ -239,7 +239,7 @@ func TestGraph(t *T) {
 
 func TestGraphImmutability(t *T) {
 	e0 := ValueOut(id("v0"), id("e0"))
-	g0 := Null.ValueIn(e0, id("v1"))
+	g0 := Null.AddValueIn(e0, id("v1"))
 	assert.Nil(t, Null.Value(id("v0")))
 	assert.Nil(t, Null.Value(id("v1")))
 	assert.NotNil(t, g0.Value(id("v0")))
@@ -247,21 +247,219 @@ func TestGraphImmutability(t *T) {
 
 	// half-edges should be re-usable
 	e1 := ValueOut(id("v2"), id("e1"))
-	g1a := g0.ValueIn(e1, id("v3a"))
-	g1b := g0.ValueIn(e1, id("v3b"))
+	g1a := g0.AddValueIn(e1, id("v3a"))
+	g1b := g0.AddValueIn(e1, id("v3b"))
 	assertVertexEqual(t, value("v3a", edge("e1", value("v2"))), g1a.Value(id("v3a")))
 	assert.Nil(t, g1a.Value(id("v3b")))
 	assertVertexEqual(t, value("v3b", edge("e1", value("v2"))), g1b.Value(id("v3b")))
 	assert.Nil(t, g1b.Value(id("v3a")))
 
 	// ... even re-usable twice in succession
-	g2 := g0.ValueIn(e1, id("v3")).ValueIn(e1, id("v4"))
+	g2 := g0.AddValueIn(e1, id("v3")).AddValueIn(e1, id("v4"))
 	assert.Nil(t, g2.Value(id("v3b")))
 	assert.Nil(t, g2.Value(id("v3a")))
 	assertVertexEqual(t, value("v3", edge("e1", value("v2"))), g2.Value(id("v3")))
 	assertVertexEqual(t, value("v4", edge("e1", value("v2"))), g2.Value(id("v4")))
 }
 
+func TestGraphDelValueIn(t *T) {
+	{ // removing from null
+		g := Null.DelValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+		assert.True(t, Equal(Null, g))
+	}
+
+	{ // removing edge from vertex which doesn't have that edge
+		g0 := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+		g1 := g0.DelValueIn(ValueOut(id("v0"), id("e1")), id("v1"))
+		assert.True(t, Equal(g0, g1))
+	}
+
+	{ // removing only edge
+		he := ValueOut(id("v0"), id("e0"))
+		g0 := Null.AddValueIn(he, id("v1"))
+		g1 := g0.DelValueIn(he, id("v1"))
+		assert.True(t, Equal(Null, g1))
+	}
+
+	{ // removing only edge (junction)
+		he := JunctionOut([]HalfEdge{
+			ValueOut(id("v0"), id("e0")),
+			ValueOut(id("v1"), id("e1")),
+		}, id("ej0"))
+		g0 := Null.AddValueIn(he, id("v2"))
+		g1 := g0.DelValueIn(he, id("v2"))
+		assert.True(t, Equal(Null, g1))
+	}
+
+	{ // removing one of two edges
+		he := ValueOut(id("v1"), id("e0"))
+		g0 := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v2"))
+		g1 := g0.AddValueIn(he, id("v2"))
+		g2 := g1.DelValueIn(he, id("v2"))
+		assert.True(t, Equal(g0, g2))
+		assert.NotNil(t, g2.Value(id("v0")))
+		assert.Nil(t, g2.Value(id("v1")))
+		assert.NotNil(t, g2.Value(id("v2")))
+	}
+
+	{ // removing one of two edges (junction)
+		e0 := ValueOut(id("v0"), id("e0"))
+		e1 := ValueOut(id("v1"), id("e1"))
+		e2 := ValueOut(id("v2"), id("e2"))
+		heA := JunctionOut([]HalfEdge{e0, e1}, id("heA"))
+		heB := JunctionOut([]HalfEdge{e1, e2}, id("heB"))
+		g0a := Null.AddValueIn(heA, id("v3"))
+		g0b := Null.AddValueIn(heB, id("v3"))
+		g1 := g0a.Union(g0b).DelValueIn(heA, id("v3"))
+		assert.True(t, Equal(g1, g0b))
+		assert.Nil(t, g1.Value(id("v0")))
+		assert.NotNil(t, g1.Value(id("v1")))
+		assert.NotNil(t, g1.Value(id("v2")))
+		assert.NotNil(t, g1.Value(id("v3")))
+	}
+
+	{ // removing one of two edges in circular graph
+		e0 := ValueOut(id("v0"), id("e0"))
+		e1 := ValueOut(id("v1"), id("e1"))
+		g0 := Null.AddValueIn(e0, id("v1")).AddValueIn(e1, id("v0"))
+		g1 := g0.DelValueIn(e0, id("v1"))
+		assert.True(t, Equal(Null.AddValueIn(e1, id("v0")), g1))
+		assert.NotNil(t, g1.Value(id("v0")))
+		assert.NotNil(t, g1.Value(id("v1")))
+	}
+
+	{ // removing to's only edge, sub-nodes have edge to each other
+		ej := JunctionOut([]HalfEdge{
+			ValueOut(id("v0"), id("ej0")),
+			ValueOut(id("v1"), id("ej0")),
+		}, id("ej"))
+		g0 := Null.AddValueIn(ej, id("v2"))
+		e0 := ValueOut(id("v0"), id("e0"))
+		g1 := g0.AddValueIn(e0, id("v1"))
+		g2 := g1.DelValueIn(ej, id("v2"))
+		assert.True(t, Equal(Null.AddValueIn(e0, id("v1")), g2))
+		assert.NotNil(t, g2.Value(id("v0")))
+		assert.NotNil(t, g2.Value(id("v1")))
+		assert.Nil(t, g2.Value(id("v2")))
+	}
+}
+
+func TestGraphUnion(t *T) {
+	assertUnion := func(g1, g2 *Graph) *Graph {
+		ga := g1.Union(g2)
+		gb := g2.Union(g1)
+		assert.True(t, Equal(ga, gb))
+		return ga
+	}
+
+	{ // Union with Null
+		assert.True(t, Equal(Null, Null.Union(Null)))
+
+		g := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+		assert.True(t, Equal(g, assertUnion(g, Null)))
+	}
+
+	{ // Two disparate graphs union'd
+		g0 := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+		g1 := Null.AddValueIn(ValueOut(id("v2"), id("e1")), id("v3"))
+		g := assertUnion(g0, g1)
+		assertVertexEqual(t, value("v0"), g.Value(id("v0")))
+		assertVertexEqual(t, value("v1", edge("e0", value("v0"))), g.Value(id("v1")))
+		assertVertexEqual(t, value("v2"), g.Value(id("v2")))
+		assertVertexEqual(t, value("v3", edge("e1", value("v2"))), g.Value(id("v3")))
+	}
+
+	{ // Two disparate graphs with junctions
+		ga := Null.AddValueIn(JunctionOut([]HalfEdge{
+			ValueOut(id("va0"), id("ea0")),
+			ValueOut(id("va1"), id("ea1")),
+		}, id("eaj")), id("va2"))
+		gb := Null.AddValueIn(JunctionOut([]HalfEdge{
+			ValueOut(id("vb0"), id("eb0")),
+			ValueOut(id("vb1"), id("eb1")),
+		}, id("ebj")), id("vb2"))
+		g := assertUnion(ga, gb)
+		assertVertexEqual(t, value("va0"), g.Value(id("va0")))
+		assertVertexEqual(t, value("va1"), g.Value(id("va1")))
+		assertVertexEqual(t,
+			value("va2", junction("eaj",
+				edge("ea0", value("va0")),
+				edge("ea1", value("va1")))),
+			g.Value(id("va2")),
+		)
+		assertVertexEqual(t, value("vb0"), g.Value(id("vb0")))
+		assertVertexEqual(t, value("vb1"), g.Value(id("vb1")))
+		assertVertexEqual(t,
+			value("vb2", junction("ebj",
+				edge("eb0", value("vb0")),
+				edge("eb1", value("vb1")))),
+			g.Value(id("vb2")),
+		)
+	}
+
+	{ // Two partially overlapping graphs
+		g0 := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v2"))
+		g1 := Null.AddValueIn(ValueOut(id("v1"), id("e1")), id("v2"))
+		g := assertUnion(g0, g1)
+		assertVertexEqual(t, value("v0"), g.Value(id("v0")))
+		assertVertexEqual(t, value("v1"), g.Value(id("v1")))
+		assertVertexEqual(t,
+			value("v2",
+				edge("e0", value("v0")),
+				edge("e1", value("v1")),
+			),
+			g.Value(id("v2")),
+		)
+	}
+
+	{ // two partially overlapping graphs with junctions
+		g0 := Null.AddValueIn(JunctionOut([]HalfEdge{
+			ValueOut(id("v0"), id("e0")),
+			ValueOut(id("v1"), id("e1")),
+		}, id("ej0")), id("v2"))
+		g1 := Null.AddValueIn(JunctionOut([]HalfEdge{
+			ValueOut(id("v0"), id("e0")),
+			ValueOut(id("v1"), id("e1")),
+		}, id("ej1")), id("v2"))
+		g := assertUnion(g0, g1)
+		assertVertexEqual(t, value("v0"), g.Value(id("v0")))
+		assertVertexEqual(t, value("v1"), g.Value(id("v1")))
+		assertVertexEqual(t,
+			value("v2",
+				junction("ej0", edge("e0", value("v0")), edge("e1", value("v1"))),
+				junction("ej1", edge("e0", value("v0")), edge("e1", value("v1"))),
+			),
+			g.Value(id("v2")),
+		)
+	}
+
+	{ // Two equal graphs
+		g0 := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+		g := assertUnion(g0, g0)
+		assertVertexEqual(t, value("v0"), g.Value(id("v0")))
+		assertVertexEqual(t,
+			value("v1", edge("e0", value("v0"))),
+			g.Value(id("v1")),
+		)
+	}
+
+	{ // Two equal graphs with junctions
+		g0 := Null.AddValueIn(JunctionOut([]HalfEdge{
+			ValueOut(id("v0"), id("e0")),
+			ValueOut(id("v1"), id("e1")),
+		}, id("ej0")), id("v2"))
+		g := assertUnion(g0, g0)
+		assertVertexEqual(t, value("v0"), g.Value(id("v0")))
+		assertVertexEqual(t, value("v1"), g.Value(id("v1")))
+		assertVertexEqual(t,
+			value("v2",
+				junction("ej0", edge("e0", value("v0")), edge("e1", value("v1"))),
+			),
+			g.Value(id("v2")),
+		)
+	}
+}
+
 func TestGraphEqual(t *T) {
 	assertEqual := func(g1, g2 *Graph) {
 		assert.True(t, Equal(g1, g2))
@@ -278,32 +476,32 @@ func TestGraphEqual(t *T) {
 	{
 		// graph is equal to itself, not to null
 		e0 := ValueOut(id("v0"), id("e0"))
-		g0 := Null.ValueIn(e0, id("v1"))
+		g0 := Null.AddValueIn(e0, id("v1"))
 		assertNotEqual(g0, Null)
 		assertEqual(g0, g0)
 
 		// adding the an existing edge again shouldn't do anything
-		assertEqual(g0, g0.ValueIn(e0, id("v1")))
+		assertEqual(g0, g0.AddValueIn(e0, id("v1")))
 
 		// g1a and g1b have the same vertices, but the edges are different
-		g1a := g0.ValueIn(ValueOut(id("v0"), id("e1a")), id("v2"))
-		g1b := g0.ValueIn(ValueOut(id("v0"), id("e1b")), id("v2"))
+		g1a := g0.AddValueIn(ValueOut(id("v0"), id("e1a")), id("v2"))
+		g1b := g0.AddValueIn(ValueOut(id("v0"), id("e1b")), id("v2"))
 		assertNotEqual(g1a, g1b)
 	}
 
 	{ // equal construction should yield equality, even if out of order
-		ga := Null.ValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
-		ga = ga.ValueIn(ValueOut(id("v1"), id("e1")), id("v2"))
-		gb := Null.ValueIn(ValueOut(id("v1"), id("e1")), id("v2"))
-		gb = gb.ValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+		ga := Null.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
+		ga = ga.AddValueIn(ValueOut(id("v1"), id("e1")), id("v2"))
+		gb := Null.AddValueIn(ValueOut(id("v1"), id("e1")), id("v2"))
+		gb = gb.AddValueIn(ValueOut(id("v0"), id("e0")), id("v1"))
 		assertEqual(ga, gb)
 	}
 
 	{ // junction basic test
 		e0 := ValueOut(id("v0"), id("e0"))
 		e1 := ValueOut(id("v1"), id("e1"))
-		ga := Null.ValueIn(JunctionOut([]HalfEdge{e0, e1}, id("ej")), id("v2"))
-		gb := Null.ValueIn(JunctionOut([]HalfEdge{e1, e0}, id("ej")), id("v2"))
+		ga := Null.AddValueIn(JunctionOut([]HalfEdge{e0, e1}, id("ej")), id("v2"))
+		gb := Null.AddValueIn(JunctionOut([]HalfEdge{e1, e0}, id("ej")), id("v2"))
 		assertEqual(ga, ga)
 		assertNotEqual(ga, gb)
 	}