diff --git a/dotscape b/dotscape
index d86b965..6f58cd0 100755
Binary files a/dotscape and b/dotscape differ
diff --git a/functional-core/app-update.sml b/functional-core/app-update.sml
index d8cd667..0877e53 100644
--- a/functional-core/app-update.sml
+++ b/functional-core/app-update.sml
@@ -120,15 +120,18 @@ struct
     case #triangleStage model of
       FIRST {x1, y1} =>
         (* Change FIRST to NO_TRIANGLE and clear buttons. *)
-        let val model = AppWith.undoTriangleStage (model, NO_TRIANGLE, (x1, y1))
-        in (model, CLEAR_BUTTONS)
+        let
+          val model =
+            AppWith.undo (model, NO_TRIANGLE, #triangles model, (x1, y1))
+        in
+          (model, CLEAR_BUTTONS)
         end
     | SECOND {x1, y1, x2, y2} =>
         (* Change FIRST to SECOND and redraw buttons. *)
         let
           val newTriangleStage = FIRST {x1 = x1, y1 = y1}
           val model =
-            AppWith.undoTriangleStage (model, newTriangleStage, (x2, y2))
+            AppWith.undo (model, newTriangleStage, #triangles model, (x2, y2))
 
           val emptyVec: Real32.real vector = Vector.fromList []
           val drawVec = TriangleStage.firstToVector (x1, y1, emptyVec, model)
@@ -145,8 +148,7 @@ struct
              let
                val triangleStage = SECOND {x1 = x1, y1 = y1, x2 = x2, y2 = y2}
                val model =
-                 AppWith.undoTriangle
-                   (model, triangleStage, trianglesTl, (x3, y3))
+                 AppWith.undo (model, triangleStage, trianglesTl, (x3, y3))
 
                val newTriangleVec = Triangles.toVector model
                val drawVec = TriangleStage.secondToVector
@@ -161,6 +163,60 @@ struct
              (* Can't undo, because there are no actions to undo. *)
              (model, NO_DRAW))
 
+  fun redoAction model =
+    case #redo model of
+      (redoHd as (x, y)) :: tl =>
+        (* There is a click point to redo. *)
+        (case #triangleStage model of
+           NO_TRIANGLE =>
+             (* add to triangle stage, and redraw buttons *)
+             let
+               val newTriangleStage = FIRST {x1 = x, y1 = y}
+               val model =
+                 AppWith.redo
+                   (model, newTriangleStage, #triangles model, redoHd)
+
+               val emptyVec: Real32.real vector = Vector.fromList []
+               val drawVec =
+                 TriangleStage.firstToVector (x1, y1, emptyVec, model)
+               val drawMsg = DRAW_BUTTON drawVec
+             in
+               (model, drawMsg)
+             end
+         | FIRST {x1, y1} =>
+             (* add to triangle stage, redraw buttons *)
+             let
+               val newTriangleStage = SECOND {x1 = x1, y1 = y1, x2 = x, y2 = y}
+               val model =
+                 AppWith.redo
+                   (model, newTriangleStage, #triangles model, redoHd)
+
+               val emptyVec: Real32.real vector = Vector.fromList []
+               val drawVec = TriangleStage.secondToVector
+                 (x1, y1, x, y, emptyVec, model)
+               val drawMsg = DRAW_BUTTON drawVec
+             in
+               (model, drawMsg)
+             end
+         | SECOND {x1, y1, x2, y2} =>
+             (* clear triangle stage, add to trinagle list and redraw triangles *)
+             let
+               val newTriangleStage = NO_TRIANGLE
+               val newTriangle =
+                 {x1 = x1, y1 = y1, x2 = x2, y2 = y2, x3 = x, y3 = y}
+               val newTriangles = newUndoTuple :: (#triangles model)
+               val model =
+                 AppWith.redo (model, newTriangleStage, newTriangles, redoHd)
+
+               val drawVec = Triangles.toVector model
+               val drawMsg = DRAW_TRIANGLES_AND_RESET_BUTTONS drawVec
+             in
+               (model, drawMsg)
+             end)
+    | [] => 
+        (* Nothing to redo. *) 
+        (model, NO_DRAW)
+
   fun update (model: app_type, inputMsg) =
     case inputMsg of
       MOUSE_MOVE {x = mouseX, y = mouseY} =>
@@ -171,4 +227,5 @@ struct
     | MOUSE_LEFT_CLICK => mouseLeftClick model
     | RESIZE_WINDOW {width, height} => resizeWindow (model, width, height)
     | UNDO_ACTION => undoAction model
+    | REDO_ACTION => redoAction model
 end
diff --git a/functional-core/app-with.sml b/functional-core/app-with.sml
index e9051ab..65c5c77 100644
--- a/functional-core/app-with.sml
+++ b/functional-core/app-with.sml
@@ -5,11 +5,14 @@ sig
   val mousePosition: AppType.app_type * Real32.real * Real32.real
                      -> AppType.app_type
 
-  val undoTriangleStage:
-    AppType.app_type * AppType.triangle_stage * (Real32.real * Real32.real)
+  val undo:
+    AppType.app_type
+    * AppType.triangle_stage
+    * AppType.triangle list
+    * (Real32.real * Real32.real)
     -> AppType.app_type
 
-  val undoTriangle:
+  val redo:
     AppType.app_type
     * AppType.triangle_stage
     * AppType.triangle list
@@ -109,83 +112,6 @@ struct
       }
     end
 
-  (* add to redo, pop one from undo *)
-  fun undoTriangleStage (app: app_type, newTriangleStage, newRedoHd) =
-    let
-      val
-        { triangleStage = _
-        , triangles
-        , xClickPoints
-        , yClickPoints
-        , windowWidth
-        , windowHeight
-        , graphLines
-        , undo
-        , redo
-        , mouseX
-        , mouseY
-        } = app
-
-      val newUndo =
-        case undo of
-          hd :: tl => tl
-        | empty => empty
-
-      val newRedo = newRedoHd :: redo
-    in
-      { triangleStage = newTriangleStage
-      , triangles = triangles
-      , undo = newUndo
-      , redo = newRedo
-      , xClickPoints = xClickPoints
-      , yClickPoints = yClickPoints
-      , windowWidth = windowWidth
-      , windowHeight = windowHeight
-      , graphLines = graphLines
-      , mouseX = mouseX
-      , mouseY = mouseY
-      }
-    end
-
-  fun undoTriangle
-    (app: app_type, newTriangleStage: triangle_stage, trianglesTl, newRedoHd) :
-    app_type =
-    let
-      val
-        { triangleStage = _
-        , triangles = _
-        , xClickPoints
-        , yClickPoints
-        , windowWidth
-        , windowHeight
-        , graphLines
-        , undo
-        , redo
-        , mouseX
-        , mouseY
-        } = app
-
-      val newUndo =
-        case undo of
-          hd :: tl => tl
-        | empty => empty
-
-      val newRedo = newRedoHd :: redo
-    in
-      { triangleStage = newTriangleStage
-      , triangles = trianglesTl
-      , undo = newUndo
-      , redo = newRedo
-      , xClickPoints = xClickPoints
-      , yClickPoints = yClickPoints
-      , windowWidth = windowWidth
-      , windowHeight = windowHeight
-      , graphLines = graphLines
-      , mouseX = mouseX
-      , mouseY = mouseY
-      }
-    end
-
   fun helpWindowResize
     (app: app_type, windowWidth, windowHeight, wStart, wFinish, hStart, hFinish) :
     app_type =
@@ -276,4 +202,79 @@ struct
       , redo = redo
       }
     end
+
+  (* add to redo, pop one from undo *)
+  fun undo (app: app_type, newTriangleStage, newTriangles, newRedoHd) =
+    let
+      val
+        { triangleStage = _
+        , triangles = _
+        , xClickPoints
+        , yClickPoints
+        , windowWidth
+        , windowHeight
+        , graphLines
+        , undo
+        , redo
+        , mouseX
+        , mouseY
+        } = app
+
+      val newUndo =
+        case undo of
+          hd :: tl => tl
+        | empty => empty
+
+      val newRedo = newRedoHd :: redo
+    in
+      { triangleStage = newTriangleStage
+      , triangles = newTriangles
+      , undo = newUndo
+      , redo = newRedo
+      , xClickPoints = xClickPoints
+      , yClickPoints = yClickPoints
+      , windowWidth = windowWidth
+      , windowHeight = windowHeight
+      , graphLines = graphLines
+      , mouseX = mouseX
+      , mouseY = mouseY
+      }
+    end
+
+  (* add to undo, pop one from redo *)
+  fun redo (app: app_type, newTriangleStage, newTriangles, newUndoHd) =
+    let
+      val
+        { triangleStage = _
+        , triangles = _
+        , xClickPoints
+        , yClickPoints
+        , windowWidth
+        , windowHeight
+        , graphLines
+        , undo
+        , redo
+        , mouseX
+        , mouseY
+        } = app
+
+      val newUndo = newUndoHd :: undo
+      val newRedo =
+        case redo of
+          hd :: tl => tl
+        | empty => empty
+    in
+      { triangleStage = newTriangleStage
+      , triangles = newTriangles
+      , undo = newUndo
+      , redo = newRedo
+      , xClickPoints = xClickPoints
+      , yClickPoints = yClickPoints
+      , windowWidth = windowWidth
+      , windowHeight = windowHeight
+      , graphLines = graphLines
+      , mouseX = mouseX
+      , mouseY = mouseY
+      }
+    end
 end
diff --git a/message-types/input-msg.sml b/message-types/input-msg.sml
index 3f2ce1a..4f8b6f2 100644
--- a/message-types/input-msg.sml
+++ b/message-types/input-msg.sml
@@ -6,6 +6,7 @@ sig
   | MOUSE_LEFT_RELEASE
   | RESIZE_WINDOW of {width: int, height: int}
   | UNDO_ACTION
+  | REDO_ACTION
 end
 
 structure InputMessage :> INPUT_MESSAGE =
@@ -16,4 +17,5 @@ struct
   | MOUSE_LEFT_RELEASE
   | RESIZE_WINDOW of {width: int, height: int}
   | UNDO_ACTION
+  | REDO_ACTION
 end