diff --git a/attr.go b/attr.go
index b31bdc3..2eed381 100644
--- a/attr.go
+++ b/attr.go
@@ -34,7 +34,10 @@ func (a Attrs) String() string {
 	}
 	elems := []string{}
 	for key, val := range a {
-		elems = append(elems, fmt.Sprintf("%v:%v", key, val))
+		valStr := fmt.Sprintf("%v", val)
+		if valStr != "" {
+			elems = append(elems, fmt.Sprintf("%s:%s", key, valStr))
+		}
 	}
 	sort.Strings(elems)
 	return fmt.Sprintf("[%s]", strings.Join(elems, ","))
diff --git a/edge.go b/edge.go
index c00581b..2cf9bc3 100644
--- a/edge.go
+++ b/edge.go
@@ -2,12 +2,18 @@ package graphman
 
 import (
 	"fmt"
+	"sort"
 	"strings"
 )
 
+//
+// Edge
+//
+
 type Edge struct {
-	src *Vertex
-	dst *Vertex
+	src     *Vertex
+	dst     *Vertex
+	deleted bool // temporary variable used by gc()
 	Attrs
 }
 
@@ -56,8 +62,22 @@ func (e *Edge) OtherVertex(id string) *Vertex {
 	return nil
 }
 
+//
+// Edges
+//
+
 type Edges []*Edge
 
+func (e Edges) filtered() Edges {
+	filtered := Edges{}
+	for _, edge := range e {
+		if !edge.deleted {
+			filtered = append(filtered, edge)
+		}
+	}
+	return filtered
+}
+
 func (e Edges) String() string {
 	items := []string{}
 	for _, edge := range e {
@@ -65,3 +85,52 @@ func (e Edges) String() string {
 	}
 	return fmt.Sprintf("{%s}", strings.Join(items, ","))
 }
+
+func (e Edges) Equals(other Edges) bool {
+	tmp := map[*Edge]int{}
+	for _, edge := range e {
+		tmp[edge]++
+	}
+	for _, edge := range other {
+		tmp[edge]--
+	}
+	for _, v := range tmp {
+		if v != 0 {
+			return false
+		}
+	}
+	return true
+}
+
+// AllCombinations returns the different combinations of Edges in a group of Edges
+//
+// Adapted from https://github.com/mxschmitt/golang-combinations
+func (e Edges) AllCombinations() EdgesCombinations {
+	combinations := EdgesCombinations{}
+	length := uint(len(e))
+
+	for combinationBits := 1; combinationBits < (1 << length); combinationBits++ {
+		var combination Edges
+		for object := uint(0); object < length; object++ {
+			if (combinationBits>>object)&1 == 1 {
+				combination = append(combination, e[object])
+			}
+		}
+		combinations = append(combinations, combination)
+	}
+
+	return combinations
+}
+
+//
+// EdgesCombinations
+//
+
+type EdgesCombinations []Edges
+
+func (ec EdgesCombinations) LongestToShortest() EdgesCombinations {
+	sort.Slice(ec, func(i, j int) bool {
+		return len(ec[i]) > len(ec[j])
+	})
+	return ec
+}
diff --git a/examples/pertify/la-methode-pert-p101.yml b/examples/pertify/la-methode-pert-p101.yml
index a1501cd..c033e57 100644
--- a/examples/pertify/la-methode-pert-p101.yml
+++ b/examples/pertify/la-methode-pert-p101.yml
@@ -3,59 +3,79 @@
 actions:
   - id: "a"
     estimate: [7]
+    title: "a"
   - id: "b"
+    title: "b"
     estimate: [8]
   - id: "c"
+    title: "c"
     estimate: [9]
   - id: "d"
+    title: "d"
     estimate: [10]
     depends_on: ["a", "e"]
   - id: "e"
+    title: "e"
     estimate: [2]
     depends_on: ["b", "f"]
   - id: "f"
+    title: "f"
     estimate: [6]
     depends_on: ["c"]
   - id: "g"
+    title: "g"
     estimate: [14]
     depends_on: ["b", "f"]
   - id: "h"
+    title: "h"
     estimate: [7]
     depends_on: ["b", "f"]
   - id: "i"
+    title: "i"
     estimate: [6]
     depends_on: ["b", "f"]
   - id: "j"
+    title: "j"
     estimate: [5]
     depends_on: ["c"]
   - id: "k"
+    title: "k"
     estimate: [2]
     depends_on: ["c"]
   - id: "l"
+    title: "l"
     estimate: [2]
     depends_on: ["d", "g"]
   - id: "m"
+    title: "m"
     estimate: [18]
     depends_on: ["l", "h"]
   - id: "n"
+    title: "n"
     estimate: [9]
     depends_on: ["i", "j"]
   - id: "o"
+    title: "o"
     estimate: [16]
     depends_on: ["k"]
   - id: "p"
+    title: "p"
     estimate: [21]
     depends_on: ["k"]
   - id: "q"
+    title: "q"
     estimate: [9]
     depends_on: ["m", "r"]
   - id: "r"
+    title: "r"
     estimate: [12]
     depends_on: ["n", "o"]
   - id: "s"
+    title: "s"
     estimate: [14]
     depends_on: ["p"]
   - id: "t"
+    title: "t"
     estimate: [6]
     depends_on: ["s"]
 
diff --git a/examples/pertify/pert-and-cpm-p35.yml b/examples/pertify/pert-and-cpm-p35.yml
new file mode 100644
index 0000000..849918e
--- /dev/null
+++ b/examples/pertify/pert-and-cpm-p35.yml
@@ -0,0 +1,47 @@
+actions:
+  - id: A
+    title: A
+  - id: B
+    title: B
+  - id: C
+    title: C
+  - id: D
+    title: D
+    depends_on: ["3"]
+  - id: E
+    title: E
+    depends_on: ["4"]
+  - id: F
+    title: F
+    depends_on: ["5"]
+  - id: G
+    title: G
+    depends_on: ["6"]
+  - id: H
+    title: H
+  - id: I
+    title: I
+    depends_on: ["7"]
+
+states:
+  - id: "1"
+    title: "1"
+    depends_on: ["A"]
+  - id: "2"
+    title: "2"
+    depends_on: ["B"]
+  - id: "3"
+    title: "3"
+    depends_on: ["C", "1"]
+  - id: "4"
+    title: "4"
+    depends_on: ["1", "2"]
+  - id: "5"
+    title: "5"
+    depends_on: ["1", "2"]
+  - id: "6"
+    title: "6"
+    depends_on: ["1", "2"]
+  - id: "7"
+    title: "7"
+    depends_on: ["2", "H"]
diff --git a/graph.go b/graph.go
index 972473a..da7f77c 100644
--- a/graph.go
+++ b/graph.go
@@ -40,7 +40,7 @@ func (g Graph) SinkVertices() Vertices {
 			sinks = append(sinks, vertex)
 		}
 	}
-	return sinks
+	return sinks.filtered()
 }
 
 func (g Graph) ConnectedSubgraphs() Graphs {
@@ -81,7 +81,7 @@ func (g Graph) ConnectedSubgraphFromVertex(start *Vertex) *Graph {
 func (g Graph) SourceVertices() Vertices {
 	sources := Vertices{}
 	for _, vertex := range g.vertices {
-		if vertex.IsSource() {
+		if !vertex.deleted && vertex.IsSource() {
 			sources = append(sources, vertex)
 		}
 	}
@@ -186,7 +186,32 @@ func (g Graph) Edges() Edges {
 
 func (g Graph) Vertices() Vertices {
 	sort.Sort(g.vertices)
-	return g.vertices
+	return g.vertices.filtered()
+}
+
+func (g *Graph) gc() uint {
+	removed := uint(0)
+	verticesToDelete := Vertices{}
+	for _, vertex := range g.vertices {
+		if vertex.deleted {
+			verticesToDelete = append(verticesToDelete, vertex)
+		}
+	}
+	edgesToDelete := Edges{}
+	for _, edge := range g.edges {
+		if edge.deleted {
+			edgesToDelete = append(edgesToDelete, edge)
+		}
+	}
+	for _, edge := range edgesToDelete {
+		removed++
+		g.RemoveEdge(edge.src.id, edge.dst.id)
+	}
+	for _, vertex := range verticesToDelete {
+		removed++
+		g.RemoveVertex(vertex.id)
+	}
+	return removed
 }
 
 func (g *Graph) AddVertex(id string, attrs ...Attrs) *Vertex {
@@ -211,6 +236,7 @@ func (g *Graph) AddVertex(id string, attrs ...Attrs) *Vertex {
 func (g *Graph) RemoveVertex(id string) bool {
 	for k, v := range g.vertices {
 		if v.id == id {
+			v.deleted = true
 			g.vertices = append(g.vertices[:k], g.vertices[k+1:]...)
 			return true
 		}
@@ -219,8 +245,9 @@ func (g *Graph) RemoveVertex(id string) bool {
 }
 
 func (g *Graph) RemoveEdge(src, dst string) bool {
-	for k, v := range g.edges {
-		if v.src.id == src && v.dst.id == dst {
+	for k, e := range g.edges {
+		if e.src.id == src && e.dst.id == dst {
+			e.deleted = true
 			g.edges = append(g.edges[:k], g.edges[k+1:]...)
 			return true
 		}
diff --git a/pert_config.go b/pert_config.go
index 6d531c0..511e87c 100644
--- a/pert_config.go
+++ b/pert_config.go
@@ -3,6 +3,7 @@ package graphman
 import (
 	"fmt"
 	"log"
+	"strings"
 )
 
 type PertAction struct {
@@ -45,7 +46,7 @@ func FromPertConfig(config PertConfig) *Graph {
 		graph.AddVertex(state.ID, attrs)
 		for _, dependency := range state.DependsOn {
 			graph.AddEdge(
-				pertPostID(dependency),
+				graph.pertGetDependencyEnd(dependency),
 				state.ID,
 				Attrs{}.SetPertZeroTimeActivity(),
 			)
@@ -80,9 +81,10 @@ func FromPertConfig(config PertConfig) *Graph {
 			)
 		case 1: // only one dependency
 			dependency := action.DependsOn[0]
+
 			graph.AddEdge(
-				pertPostID(dependency),
-				pertPreID(action.ID),
+				graph.pertGetDependencyEnd(dependency),
+				pertPostID(action.ID),
 				attrs,
 			)
 		default:
@@ -93,7 +95,7 @@ func FromPertConfig(config PertConfig) *Graph {
 			)
 			for _, dependency := range action.DependsOn {
 				graph.AddEdge(
-					pertPostID(dependency),
+					graph.pertGetDependencyEnd(dependency),
 					pertPreID(action.ID),
 					Attrs{}.SetPertZeroTimeActivity(),
 				)
@@ -124,37 +126,124 @@ func FromPertConfig(config PertConfig) *Graph {
 	}
 
 	for _, vertex := range graph.Vertices() {
-		if vertex.Attrs.GetTitle() == "" {
+		if !pertIsUntitledState(vertex) && vertex.Attrs.GetTitle() == "" {
 			vertex.Attrs.SetTitle(vertex.id)
 		}
 	}
 	if !config.Opts.NoSimplify { // simplify the graph
-		verticesToDelete := map[string]bool{} // creating a map so we can iterate over vertices while deleting some entries
-		for _, vertex := range graph.Vertices() {
-			if pertIsUntitledState(vertex) || true {
-				if vertex.OutDegree() == 1 { // remove dummy states with only one dummy successor
-					successor := vertex.SuccessorEdges()[0]
-					if pertIsZeroTimeActivity(successor) {
-						for _, predecessor := range vertex.PredecessorEdges() {
-							predecessor.dst = successor.dst
-						}
-						graph.RemoveEdge(vertex.id, successor.dst.id)
-						verticesToDelete[vertex.id] = true
-					}
-				}
+		for {
+			pertRemoveDummySteps(graph)
+			pertMergeDummyActionGroups(graph)
+			if removed := graph.gc(); removed == 0 {
+				break
 			}
 		}
-		for id := range verticesToDelete {
-			graph.RemoveVertex(id)
-		}
 	}
 
 	return graph
 }
 
+func pertRemoveDummySteps(graph *Graph) {
+	// remove dummy states with only one dummy successor
+	for _, vertex := range graph.Vertices() {
+		if vertex.deleted || !pertIsUntitledState(vertex) || vertex.OutDegree() != 1 {
+			continue
+		}
+		successor := vertex.SuccessorEdges()[0]
+		if pertIsZeroTimeActivity(successor) {
+			for _, predecessor := range vertex.PredecessorEdges() {
+				predecessor.dst = successor.dst
+			}
+			graph.RemoveEdge(vertex.id, successor.dst.id)
+			vertex.deleted = true
+		}
+	}
+}
+
+func pertMergeDummyActionGroups(graph *Graph) {
+	// merge dummy action groups
+	for _, vertex := range graph.Vertices() {
+		if vertex.deleted || vertex.OutDegree() < 2 {
+			continue
+		}
+		for _, combination := range vertex.SuccessorEdges().AllCombinations().LongestToShortest() {
+			if len(combination) < 2 {
+				continue
+			}
+			onlyActiveDummies := true
+			for _, edge := range combination {
+				if edge.deleted || edge.src.deleted || edge.dst.deleted || !pertIsZeroTimeActivity(edge) {
+					onlyActiveDummies = false
+					break
+				}
+			}
+			if !onlyActiveDummies {
+				continue
+			}
+			predecessors := combination[0].dst.PredecessorVertices()
+			same := true
+			for i := 1; i < len(combination); i++ {
+				if !predecessors.Equals(combination[i].dst.PredecessorVertices()) {
+					same = false
+					break
+				}
+			}
+			if !same {
+				continue
+			}
+			successors := Vertices{}
+			for _, edge := range combination {
+				successors = append(successors, edge.dst)
+			}
+			predecessors = predecessors.Unique()
+			successors = successors.Unique()
+
+			ids := []string{}
+			titles := []string{}
+			for _, successor := range successors {
+				ids = append(ids, successor.id)
+				if title := successor.Attrs.GetTitle(); title != "" {
+					titles = append(titles, title)
+				}
+			}
+			metaID := strings.Join(ids, ",")
+			attrs := Attrs{}
+			if len(titles) > 0 {
+				attrs.SetTitle(strings.Join(titles, " + "))
+			} else {
+				attrs.SetPertUntitledState()
+			}
+			metaVertex := graph.AddVertex(metaID, attrs)
+			for _, predecessor := range predecessors {
+				depID := graph.pertGetDependencyEnd(predecessor.id)
+				graph.AddEdge(depID, metaID, Attrs{}.SetPertZeroTimeActivity())
+			}
+			for _, successor := range successors {
+				for _, successorSuccessor := range successor.successors {
+					successorSuccessor.src = metaVertex
+				}
+				for _, predecessor := range predecessors {
+					graph.RemoveEdge(predecessor.id, successor.id)
+				}
+				successor.deleted = true
+			}
+			break
+		}
+	}
+}
+
 func pertPreID(id string) string  { return fmt.Sprintf("pre_%s", id) }
 func pertPostID(id string) string { return fmt.Sprintf("post_%s", id) }
 
+func (g *Graph) pertGetDependencyEnd(dependency string) string {
+	// if dependency is a vertex, the end is the vertex itself
+	if vertex := g.GetVertex(dependency); vertex != nil {
+		return vertex.id
+	}
+	// else, we need to take the post_{edge}
+	return pertPostID(dependency)
+}
+
 func pertIsZeroTimeActivity(edge *Edge) bool {
 	pert := edge.GetPert()
 	return pert != nil && pert.IsZeroTimeActivity
diff --git a/pert_config_test.go b/pert_config_test.go
index 7003b75..c62e048 100644
--- a/pert_config_test.go
+++ b/pert_config_test.go
@@ -55,5 +55,5 @@ actions:
 	graph := FromPertConfig(config)
 	fmt.Println(graph)
 	// Output:
-	// {(Start,pre_5)[[pert:To=4,Tm=6,Tp=10,Te=6.33,σe=1,Ve=1,title:Prepare foundation]],(Start,pre_5)[[pert:To=2,Tm=4,Tp=7,Te=4.17,σe=0.83,Ve=0.69,title:Make & position door frames]],(Start,pre_9)[[pert:To=7,Tm=9,Tp=12,Te=9.17,σe=0.83,Ve=0.69,title:Lay drains & floor base]],(post_5,Finish)[[pert:To=2,Tm=4,Tp=5,Te=3.83,σe=0.5,Ve=0.25,title:Install service & settings]],(pre_5,post_5)[[pert:To=7,Tm=10,Tp=15,Te=10.33,σe=1.33,Ve=1.78,title:Erect walls]],(pre_6,pre_9)[[pert:To=1,Tm=2,Tp=4,Te=2.17,σe=0.5,Ve=0.25,title:Plaster ceilings]],(post_7,pre_6)[[pert:]],(post_5,Finish)[[pert:To=4,Tm=6,Tp=8,Te=6,σe=0.67,Ve=0.44,title:Erect roof]],(post_7,Finish)[[pert:To=7,Tm=9,Tp=11,Te=9,σe=0.67,Ve=0.44,title:Install door & windows]],(pre_9,pre_10)[[pert:To=1,Tm=2,Tp=3,Te=2,σe=0.33,Ve=0.11,title:Fit gutters & pipes]],(pre_10,Finish)[[pert:To=1,Tm=2,Tp=3,Te=2,σe=0.33,Ve=0.11,title:Paint outside]]}
+	// {(Start,pre_5)[[pert:To=4,Tm=6,Tp=10,Te=6.33,σe=1,Ve=1,title:Prepare foundation]],(Start,pre_5)[[pert:To=2,Tm=4,Tp=7,Te=4.17,σe=0.83,Ve=0.69,title:Make & position door frames]],(Start,pre_9)[[pert:To=7,Tm=9,Tp=12,Te=9.17,σe=0.83,Ve=0.69,title:Lay drains & floor base]],(post_5,pre_6)[[pert:To=2,Tm=4,Tp=5,Te=3.83,σe=0.5,Ve=0.25,title:Install service & settings]],(pre_5,post_5)[[pert:To=7,Tm=10,Tp=15,Te=10.33,σe=1.33,Ve=1.78,title:Erect walls]],(pre_6,pre_9)[[pert:To=1,Tm=2,Tp=4,Te=2.17,σe=0.5,Ve=0.25,title:Plaster ceilings]],(post_7,pre_6)[[]],(post_5,post_7)[[pert:To=4,Tm=6,Tp=8,Te=6,σe=0.67,Ve=0.44,title:Erect roof]],(post_7,pre_10)[[pert:To=7,Tm=9,Tp=11,Te=9,σe=0.67,Ve=0.44,title:Install door & windows]],(pre_9,pre_10)[[pert:To=1,Tm=2,Tp=3,Te=2,σe=0.33,Ve=0.11,title:Fit gutters & pipes]],(pre_10,Finish)[[pert:To=1,Tm=2,Tp=3,Te=2,σe=0.33,Ve=0.11,title:Paint outside]],Finish}
 }
diff --git a/vertex.go b/vertex.go
index 8f1a6ee..52d3342 100644
--- a/vertex.go
+++ b/vertex.go
@@ -20,6 +20,7 @@ type Vertex struct {
 		prev    *Edge
 		visited bool
 	}
+	deleted bool // temporary variable used before a gc()
 }
 
 func newVertex(id string, attrs ...Attrs) *Vertex {
@@ -39,16 +40,19 @@ func newVertex(id string, attrs ...Attrs) *Vertex {
 
 func (v Vertex) IsSource() bool          { return v.InDegree() == 0 }
 func (v Vertex) IsSink() bool            { return v.OutDegree() == 0 }
-func (v Vertex) InDegree() int           { return len(v.predecessors) }
-func (v Vertex) OutDegree() int          { return len(v.successors) }
+func (v Vertex) InDegree() int           { return len(v.PredecessorEdges()) }
+func (v Vertex) OutDegree() int          { return len(v.SuccessorEdges()) }
 func (v Vertex) Degree() int             { return v.InDegree() + v.OutDegree() }
-func (v Vertex) PredecessorEdges() Edges { return v.predecessors }
-func (v Vertex) SuccessorEdges() Edges   { return v.successors }
+func (v Vertex) PredecessorEdges() Edges { return v.predecessors.filtered() }
+func (v Vertex) SuccessorEdges() Edges   { return v.successors.filtered() }
+func (v Vertex) IsIsolated() bool        { return v.Degree() == 0 }
 
 func (v Vertex) PredecessorVertices() Vertices {
 	vertices := Vertices{}
 	for _, edge := range v.predecessors {
-		vertices = append(vertices, edge.src)
+		if !edge.deleted && !edge.src.deleted {
+			vertices = append(vertices, edge.src)
+		}
 	}
 	return vertices.Unique()
 }
@@ -56,26 +60,28 @@ func (v Vertex) PredecessorVertices() Vertices {
 func (v Vertex) SuccessorVertices() Vertices {
 	vertices := Vertices{}
 	for _, edge := range v.successors {
-		vertices = append(vertices, edge.dst)
+		if !edge.deleted && !edge.dst.deleted {
+			vertices = append(vertices, edge.dst)
+		}
 	}
 	return vertices.Unique()
 }
 
-func (v Vertex) IsIsolated() bool {
-	return len(v.predecessors) == 0 && len(v.successors) == 0
-}
-
 func (v Vertex) Edges() Edges {
-	return append(v.predecessors, v.successors...)
+	return append(v.predecessors, v.successors...).filtered()
 }
 
 func (v Vertex) Neighbors() Vertices {
 	neighbors := Vertices{}
 	for _, edge := range v.predecessors {
-		neighbors = append(neighbors, edge.src)
+		if !edge.deleted && !edge.src.deleted {
+			neighbors = append(neighbors, edge.src)
+		}
 	}
 	for _, edge := range v.successors {
-		neighbors = append(neighbors, edge.dst)
+		if !edge.deleted && !edge.dst.deleted {
+			neighbors = append(neighbors, edge.dst)
+		}
 	}
 	return neighbors.Unique()
 }
@@ -98,6 +104,9 @@ func (v *Vertex) WalkSuccessorVertices(fn VerticesWalkFunc) error {
 }
 
 func (v *Vertex) walkSuccessorVerticesRec(fn VerticesWalkFunc, previous *Vertex, depth int, visited map[string]bool) error {
+	if v.deleted {
+		return nil
+	}
 	if visited[v.id] {
 		return nil
 	}
@@ -105,7 +114,7 @@ func (v *Vertex) walkSuccessorVerticesRec(fn VerticesWalkFunc, previous *Vertex,
 	if err := fn(v, previous, depth); err != nil {
 		return err
 	}
-	for _, successor := range v.successors {
+	for _, successor := range v.SuccessorEdges() {
 		if err := successor.dst.walkSuccessorVerticesRec(fn, v, depth+1, visited); err != nil {
 			return err
 		}
@@ -119,6 +128,9 @@ func (v *Vertex) WalkPredecessorVertices(fn VerticesWalkFunc) error {
 }
 
 func (v *Vertex) walkPredecessorVerticesRec(fn VerticesWalkFunc, previous *Vertex, depth int, visited map[string]bool) error {
+	if v.deleted {
+		return nil
+	}
 	if visited[v.id] {
 		return nil
 	}
@@ -126,7 +138,7 @@ func (v *Vertex) walkPredecessorVerticesRec(fn VerticesWalkFunc, previous *Verte
 	if err := fn(v, previous, depth); err != nil {
 		return err
 	}
-	for _, predecessor := range v.predecessors {
+	for _, predecessor := range v.PredecessorEdges() {
 		if err := predecessor.dst.walkPredecessorVerticesRec(fn, v, depth+1, visited); err != nil {
 			return err
 		}
@@ -140,6 +152,9 @@ func (v *Vertex) WalkAdjacentVertices(fn VerticesWalkFunc) error {
 }
 
 func (v *Vertex) walkAdjacentVerticesRec(fn VerticesWalkFunc, previous *Vertex, depth int, visited map[string]bool) error {
+	if v.deleted {
+		return nil
+	}
 	if visited[v.id] {
 		return nil
 	}
@@ -147,12 +162,12 @@ func (v *Vertex) walkAdjacentVerticesRec(fn VerticesWalkFunc, previous *Vertex,
 	if err := fn(v, previous, depth); err != nil {
 		return err
 	}
-	for _, successor := range v.successors {
+	for _, successor := range v.SuccessorEdges() {
 		if err := successor.dst.walkAdjacentVerticesRec(fn, v, depth+1, visited); err != nil {
 			return err
 		}
 	}
-	for _, predecessor := range v.predecessors {
+	for _, predecessor := range v.PredecessorEdges() {
 		if err := predecessor.src.walkAdjacentVerticesRec(fn, v, depth+1, visited); err != nil {
 			return err
 		}
@@ -178,9 +193,19 @@ func (v Vertices) Len() int           { return len(v) }
 func (v Vertices) Swap(i, j int)      { v[i], v[j] = v[j], v[i] }
 func (v Vertices) Less(i, j int) bool { return v[i].id < v[j].id }
 
+func (v Vertices) filtered() Vertices {
+	filtered := Vertices{}
+	for _, vertex := range v {
+		if !vertex.deleted {
+			filtered = append(filtered, vertex)
+		}
+	}
+	return filtered
+}
+
 func (v Vertices) Unique() Vertices {
 	m := map[string]*Vertex{}
-	for _, v := range v {
+	for _, v := range v.filtered() {
 		m[v.id] = v
 	}
 	uniques := Vertices{}
@@ -190,3 +215,19 @@ func (v Vertices) Unique() Vertices {
 	sort.Sort(uniques)
 	return uniques
 }
+
+func (v Vertices) Equals(other Vertices) bool {
+	tmp := map[*Vertex]int{}
+	for _, vertex := range v.filtered() {
+		tmp[vertex]++
+	}
+	for _, vertex := range other.filtered() {
+		tmp[vertex]--
+	}
+	for _, v := range tmp {
+		if v != 0 {
+			return false
+		}
+	}
+	return true
+}
diff --git a/viz/graphviz.go b/viz/graphviz.go
index cd330f2..33c09ad 100644
--- a/viz/graphviz.go
+++ b/viz/graphviz.go
@@ -105,8 +105,10 @@ func attrsGeneric(a graphman.Attrs, attrs map[string]string, opts *Opts) {
 			case "rankdir", "shape", "style":
 				attrs[k] = v.(string)
 			default:
-				line := fmt.Sprintf("\n%s: %v", k, v)
-				attrs[string(graphviz.Comment)] += line
+				if vStr := fmt.Sprintf("%v", v); vStr != "" {
+					line := fmt.Sprintf("\n%s: %s", k, vStr)
+					attrs[string(graphviz.Comment)] += line
+				}
 			}
 		}
 	}