Index: Application/Ringtoets/src/Application.Ringtoets.Storage/Create/IllustrationPoints/IllustrationPointNodeCreateExtensions.cs
===================================================================
diff -u -r6c55d7ddb950eb8e434b9564367bffd9788876f8 -race63dd1e2a052cb8774347958f3f2e2013c7400
--- Application/Ringtoets/src/Application.Ringtoets.Storage/Create/IllustrationPoints/IllustrationPointNodeCreateExtensions.cs	(.../IllustrationPointNodeCreateExtensions.cs)	(revision 6c55d7ddb950eb8e434b9564367bffd9788876f8)
+++ Application/Ringtoets/src/Application.Ringtoets.Storage/Create/IllustrationPoints/IllustrationPointNodeCreateExtensions.cs	(.../IllustrationPointNodeCreateExtensions.cs)	(revision ace63dd1e2a052cb8774347958f3f2e2013c7400)
@@ -44,7 +44,7 @@
         /// <returns>A new <see cref="FaultTreeIllustrationPointEntity"/>.</returns>
         /// <exception cref="ArgumentNullException">Thrown when <paramref name="illustrationPointNode"/> 
         /// is <c>null</c>.</exception>
-        /// <exception cref="InvalidOperationException">Thrown when <see cref="IllustrationPointNode.Data"/> 
+        /// <exception cref="NotSupportedException">Thrown when <see cref="IllustrationPointNode.Data"/> 
         /// is not of type <see cref="FaultTreeIllustrationPoint"/>.</exception>
         public static FaultTreeIllustrationPointEntity Create(
             this IllustrationPointNode illustrationPointNode,
@@ -58,7 +58,7 @@
             var faultTreeIllustrationPoint = illustrationPointNode.Data as FaultTreeIllustrationPoint;
             if (faultTreeIllustrationPoint == null)
             {
-                throw new InvalidOperationException($"Illustration point type '{illustrationPointNode.Data.GetType()}' is not supported.");
+                throw new NotSupportedException($"Illustration point type '{illustrationPointNode.Data.GetType()}' is not supported.");
             }
 
             FaultTreeIllustrationPointEntity entity = CreateFaultTreeIllustrationPoint(faultTreeIllustrationPoint,
Index: Application/Ringtoets/src/Application.Ringtoets.Storage/Read/IllustrationPoints/FaultTreeIllustrationPointEntityReadExtensions.cs
===================================================================
diff -u -r70dd51c2b1d7239cc5cf4e929017308fe64e5aa9 -race63dd1e2a052cb8774347958f3f2e2013c7400
--- Application/Ringtoets/src/Application.Ringtoets.Storage/Read/IllustrationPoints/FaultTreeIllustrationPointEntityReadExtensions.cs	(.../FaultTreeIllustrationPointEntityReadExtensions.cs)	(revision 70dd51c2b1d7239cc5cf4e929017308fe64e5aa9)
+++ Application/Ringtoets/src/Application.Ringtoets.Storage/Read/IllustrationPoints/FaultTreeIllustrationPointEntityReadExtensions.cs	(.../FaultTreeIllustrationPointEntityReadExtensions.cs)	(revision ace63dd1e2a052cb8774347958f3f2e2013c7400)
@@ -105,9 +105,7 @@
 
         private static CombinationType GetCombinationType(FaultTreeIllustrationPointEntity entity)
         {
-            return entity.CombinationType == (byte) CombinationType.And
-                       ? CombinationType.And
-                       : CombinationType.Or;
+            return (CombinationType) entity.CombinationType;
         }
 
         private static IEnumerable<Stochast> GetReadStochasts(IEnumerable<StochastEntity> stochastEntities)
Index: Application/Ringtoets/src/Application.Ringtoets.Storage/Read/IllustrationPoints/GeneralResultFaultTreeIllustrationPointEntityReadExtensions.cs
===================================================================
diff -u -r283d7e09d084caafac590fdf96bfc6a264604016 -race63dd1e2a052cb8774347958f3f2e2013c7400
--- Application/Ringtoets/src/Application.Ringtoets.Storage/Read/IllustrationPoints/GeneralResultFaultTreeIllustrationPointEntityReadExtensions.cs	(.../GeneralResultFaultTreeIllustrationPointEntityReadExtensions.cs)	(revision 283d7e09d084caafac590fdf96bfc6a264604016)
+++ Application/Ringtoets/src/Application.Ringtoets.Storage/Read/IllustrationPoints/GeneralResultFaultTreeIllustrationPointEntityReadExtensions.cs	(.../GeneralResultFaultTreeIllustrationPointEntityReadExtensions.cs)	(revision ace63dd1e2a052cb8774347958f3f2e2013c7400)
@@ -54,12 +54,12 @@
 
             IEnumerable<Stochast> stochasts = GetReadStochasts(entity.StochastEntities);
 
-            IEnumerable<TopLevelFaultTreeIllustrationPoint> illustrationPoints =
+            IEnumerable<TopLevelFaultTreeIllustrationPoint> topLevelIllustrationPoints =
                 GetReadTopLevelFaultTreeIllustrationPoint(entity.TopLevelFaultTreeIllustrationPointEntities);
 
             return new GeneralResult<TopLevelFaultTreeIllustrationPoint>(governingWindDirection,
                                                                          stochasts,
-                                                                         illustrationPoints);
+                                                                         topLevelIllustrationPoints);
         }
 
         private static WindDirection GetGoverningWindDirection(IGeneralResultEntity entity)
@@ -75,10 +75,10 @@
         }
 
         private static IEnumerable<TopLevelFaultTreeIllustrationPoint> GetReadTopLevelFaultTreeIllustrationPoint(
-            IEnumerable<TopLevelFaultTreeIllustrationPointEntity> illustrationPointEntities)
+            IEnumerable<TopLevelFaultTreeIllustrationPointEntity> topLevelIllustrationPointEntities)
         {
-            return illustrationPointEntities.OrderBy(ip => ip.Order)
-                                            .Select(ip => ip.Read());
+            return topLevelIllustrationPointEntities.OrderBy(ip => ip.Order)
+                                                    .Select(ip => ip.Read());
         }
     }
 }
\ No newline at end of file
Index: Application/Ringtoets/src/Application.Ringtoets.Storage/Read/IllustrationPoints/GeneralResultSubMechanismIllustrationPointEntityReadExtensions.cs
===================================================================
diff -u -r283d7e09d084caafac590fdf96bfc6a264604016 -race63dd1e2a052cb8774347958f3f2e2013c7400
--- Application/Ringtoets/src/Application.Ringtoets.Storage/Read/IllustrationPoints/GeneralResultSubMechanismIllustrationPointEntityReadExtensions.cs	(.../GeneralResultSubMechanismIllustrationPointEntityReadExtensions.cs)	(revision 283d7e09d084caafac590fdf96bfc6a264604016)
+++ Application/Ringtoets/src/Application.Ringtoets.Storage/Read/IllustrationPoints/GeneralResultSubMechanismIllustrationPointEntityReadExtensions.cs	(.../GeneralResultSubMechanismIllustrationPointEntityReadExtensions.cs)	(revision ace63dd1e2a052cb8774347958f3f2e2013c7400)
@@ -55,12 +55,12 @@
 
             IEnumerable<Stochast> stochasts = GetReadStochasts(entity.StochastEntities);
 
-            IEnumerable<TopLevelSubMechanismIllustrationPoint> illustrationPoints =
+            IEnumerable<TopLevelSubMechanismIllustrationPoint> topLevelIllustrationPoints =
                 GetReadTopLevelSubMechanismIllustrationPoint(entity.TopLevelSubMechanismIllustrationPointEntities);
 
             return new GeneralResult<TopLevelSubMechanismIllustrationPoint>(governingWindDirection,
                                                                             stochasts,
-                                                                            illustrationPoints);
+                                                                            topLevelIllustrationPoints);
         }
 
         private static WindDirection GetGoverningWindDirection(IGeneralResultEntity entity)
@@ -76,10 +76,10 @@
         }
 
         private static IEnumerable<TopLevelSubMechanismIllustrationPoint> GetReadTopLevelSubMechanismIllustrationPoint(
-            IEnumerable<TopLevelSubMechanismIllustrationPointEntity> illustrationPointEntities)
+            IEnumerable<TopLevelSubMechanismIllustrationPointEntity> topLevelIllustrationPointEntities)
         {
-            return illustrationPointEntities.OrderBy(ip => ip.Order)
-                                            .Select(ip => ip.Read());
+            return topLevelIllustrationPointEntities.OrderBy(ip => ip.Order)
+                                                    .Select(ip => ip.Read());
         }
     }
 }
\ No newline at end of file
Index: Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Application.Ringtoets.Storage.Test.csproj
===================================================================
diff -u -raa49537188229065df91b1a931f088c32115702a -race63dd1e2a052cb8774347958f3f2e2013c7400
--- Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Application.Ringtoets.Storage.Test.csproj	(.../Application.Ringtoets.Storage.Test.csproj)	(revision aa49537188229065df91b1a931f088c32115702a)
+++ Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Application.Ringtoets.Storage.Test.csproj	(.../Application.Ringtoets.Storage.Test.csproj)	(revision ace63dd1e2a052cb8774347958f3f2e2013c7400)
@@ -97,7 +97,7 @@
     <Compile Include="Create\IllustrationPoints\SubMechanismIllustrationPointStochastCreateExtensionsTest.cs" />
     <Compile Include="Create\IllustrationPoints\StochastCreateExtensionsTest.cs" />
     <Compile Include="Create\IllustrationPoints\TopLevelFaultTreeIllustrationPointCreateExtensionsTest.cs" />
-    <Compile Include="Create\IllustrationPoints\TopLevelSubMechanismIllustrationPointTest.cs" />
+    <Compile Include="Create\IllustrationPoints\TopLevelSubMechanismIllustrationPointCreateExtensionsTest.cs" />
     <Compile Include="Create\StructuresCalculationCreateExtensionsTest.cs">
       <SubType>Code</SubType>
     </Compile>
Index: Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/GeneralResultCreateExtensionsTest.cs
===================================================================
diff -u -r6c55d7ddb950eb8e434b9564367bffd9788876f8 -race63dd1e2a052cb8774347958f3f2e2013c7400
--- Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/GeneralResultCreateExtensionsTest.cs	(.../GeneralResultCreateExtensionsTest.cs)	(revision 6c55d7ddb950eb8e434b9564367bffd9788876f8)
+++ Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/GeneralResultCreateExtensionsTest.cs	(.../GeneralResultCreateExtensionsTest.cs)	(revision ace63dd1e2a052cb8774347958f3f2e2013c7400)
@@ -279,6 +279,7 @@
             TestHelper.AssertAreEqualButNotSame(expectedWindDirection.Name, illustrationPointEntity.WindDirectionName);
             Assert.AreEqual(expectedWindDirection.Angle, illustrationPointEntity.WindDirectionAngle,
                             expectedWindDirection.Angle.GetAccuracy());
+            TestHelper.AssertAreEqualButNotSame(illustrationPoint.ClosingSituation, illustrationPointEntity.ClosingSituation);
 
             Assert.AreEqual(expectedOrder, illustrationPointEntity.Order);
         }
@@ -311,6 +312,7 @@
             TestHelper.AssertAreEqualButNotSame(expectedWindDirection.Name, illustrationPointEntity.WindDirectionName);
             Assert.AreEqual(expectedWindDirection.Angle, illustrationPointEntity.WindDirectionAngle,
                             expectedWindDirection.Angle.GetAccuracy());
+            TestHelper.AssertAreEqualButNotSame(illustrationPoint.ClosingSituation, illustrationPointEntity.ClosingSituation);
 
             Assert.AreEqual(expectedOrder, illustrationPointEntity.Order);
         }
Index: Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/IllustrationPointNodeCreateExtensionsTest.cs
===================================================================
diff -u -r79565e60750c8a6c33847cd94d5c5910b77542b1 -race63dd1e2a052cb8774347958f3f2e2013c7400
--- Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/IllustrationPointNodeCreateExtensionsTest.cs	(.../IllustrationPointNodeCreateExtensionsTest.cs)	(revision 79565e60750c8a6c33847cd94d5c5910b77542b1)
+++ Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/IllustrationPointNodeCreateExtensionsTest.cs	(.../IllustrationPointNodeCreateExtensionsTest.cs)	(revision ace63dd1e2a052cb8774347958f3f2e2013c7400)
@@ -110,16 +110,15 @@
             CollectionAssert.IsEmpty(entity.TopLevelFaultTreeIllustrationPointEntities);
             Assert.AreEqual(order, entity.Order);
 
-            StochastEntity entityStochastEntity = entity.StochastEntities.FirstOrDefault();
-            Assert.IsNotNull(entityStochastEntity);
+            StochastEntity entityStochastEntity = entity.StochastEntities.Single();
             Stochast stochast = illustrationPoint.Stochasts.First();
             Assert.AreEqual(stochast.Name, entityStochastEntity.Name);
             Assert.AreEqual(stochast.Alpha, entityStochastEntity.Alpha);
             Assert.AreEqual(stochast.Duration, entityStochastEntity.Duration);
         }
 
         [Test]
-        public void Create_IllustrationPointNodeWithSubMechanismIllustrationPoint_ThrowsInvalidOperationException()
+        public void Create_IllustrationPointNodeWithSubMechanismIllustrationPoint_ThrowsNotSupportedException()
         {
             // Setup
             var node = new IllustrationPointNode(new TestSubMechanismIllustrationPoint());
@@ -128,7 +127,7 @@
             TestDelegate call = () => node.Create(0);
 
             // Assert
-            string message = Assert.Throws<InvalidOperationException>(call).Message;
+            string message = Assert.Throws<NotSupportedException>(call).Message;
             Assert.AreEqual($"Illustration point type '{typeof(TestSubMechanismIllustrationPoint)}' is not supported.", message);
         }
 
@@ -192,17 +191,20 @@
             {
                 new IllustrationPointNode(FaultTreeIllustrationPointTestFactory.CreateTestFaultTreeIllustrationPoint()),
                 node
-            }).SetName("IllustrationPointsWithChildren");
+            }).SetName("FaultTreeIllustrationPointsWithChildren");
         }
 
         private static void AssertIllustrationPointEntities(
             IllustrationPointNode[] children,
-            IList<SubMechanismIllustrationPointEntity> subMechanismIllustrationPointEntities,
-            IList<FaultTreeIllustrationPointEntity> faultTreeIllustrationPointEntity
+            IEnumerable<SubMechanismIllustrationPointEntity> subMechanismIllustrationPointEntities,
+            IEnumerable<FaultTreeIllustrationPointEntity> faultTreeIllustrationPointEntity
         )
         {
             for (var i = 0; i < children.Length; i++)
             {
+                int nrOfTotalCreatedEntities = subMechanismIllustrationPointEntities.Count() + faultTreeIllustrationPointEntity.Count();
+                Assert.AreEqual(nrOfTotalCreatedEntities, children.Length);
+
                 IllustrationPointNode child = children[i];
 
                 var subMechanismIllustrationPoint = child.Data as SubMechanismIllustrationPoint;
@@ -231,6 +233,9 @@
             Assert.IsNotNull(illustrationPoint);
             Assert.AreEqual(illustrationPoint.Beta, illustrationPointEntity.Beta, illustrationPoint.Beta.GetAccuracy());
             TestHelper.AssertAreEqualButNotSame(illustrationPoint.Name, illustrationPointEntity.Name);
+
+            CollectionAssert.IsEmpty(illustrationPointEntity.IllustrationPointResultEntities);
+            CollectionAssert.IsEmpty(illustrationPointEntity.SubMechanismIllustrationPointStochastEntities);
         }
 
         private static void AssertFaultTreeIllustrationPointEntity(FaultTreeIllustrationPoint illustrationPoint,
Index: Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/TopLevelFaultTreeIllustrationPointCreateExtensionsTest.cs
===================================================================
diff -u -rc4289bccc81c65f0b9972d1e2d073aae31820fbf -race63dd1e2a052cb8774347958f3f2e2013c7400
--- Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/TopLevelFaultTreeIllustrationPointCreateExtensionsTest.cs	(.../TopLevelFaultTreeIllustrationPointCreateExtensionsTest.cs)	(revision c4289bccc81c65f0b9972d1e2d073aae31820fbf)
+++ Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/TopLevelFaultTreeIllustrationPointCreateExtensionsTest.cs	(.../TopLevelFaultTreeIllustrationPointCreateExtensionsTest.cs)	(revision ace63dd1e2a052cb8774347958f3f2e2013c7400)
@@ -20,6 +20,7 @@
 // All rights reserved.
 
 using System;
+using System.Linq;
 using Application.Ringtoets.Storage.Create.IllustrationPoints;
 using Application.Ringtoets.Storage.DbContext;
 using Core.Common.TestUtil;
@@ -64,7 +65,39 @@
             TestHelper.AssertAreEqualButNotSame(illustrationPoint.ClosingSituation, entity.ClosingSituation);
             TestHelper.AssertAreEqualButNotSame(windDirection.Name, entity.WindDirectionName);
             Assert.AreEqual(windDirection.Angle, entity.WindDirectionAngle, windDirection.Angle.GetAccuracy());
+            CollectionAssert.IsEmpty(illustrationPoint.FaultTreeNodeRoot.Children);
             Assert.AreEqual(order, entity.Order);
         }
+
+        [Test]
+        public void Create_ValidTopLevelFaultTreeIllustrationPointWithChildren_ReturnsTopLevelFaultTreeIllustrationPointEntityWithChildren()
+        {
+            // Setup
+            var random = new Random(21);
+
+            var windDirection = new WindDirection("WindDirection Name", random.NextDouble());
+            var topLevelIllustrationPoint = new IllustrationPointNode(FaultTreeIllustrationPointTestFactory.CreateTestFaultTreeIllustrationPoint());
+            topLevelIllustrationPoint.SetChildren(new[]
+            {
+                new IllustrationPointNode(new TestSubMechanismIllustrationPoint()),
+                new IllustrationPointNode(new TestSubMechanismIllustrationPoint())
+            });
+
+            var illustrationPoint = new TopLevelFaultTreeIllustrationPoint(
+                windDirection,
+                "Just a situation",
+                topLevelIllustrationPoint);
+            int order = random.Next();
+
+            // Call
+            TopLevelFaultTreeIllustrationPointEntity entity = illustrationPoint.Create(order);
+
+            // Assert
+            TestHelper.AssertAreEqualButNotSame(illustrationPoint.ClosingSituation, entity.ClosingSituation);
+            TestHelper.AssertAreEqualButNotSame(windDirection.Name, entity.WindDirectionName);
+            Assert.AreEqual(windDirection.Angle, entity.WindDirectionAngle, windDirection.Angle.GetAccuracy());
+            Assert.AreEqual(2, entity.FaultTreeIllustrationPointEntity.SubMechanismIllustrationPointEntities.Count);
+            Assert.AreEqual(order, entity.Order);
+        }
     }
 }
\ No newline at end of file
Index: Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/TopLevelSubMechanismIllustrationPointCreateExtensionsTest.cs
===================================================================
diff -u
--- Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/TopLevelSubMechanismIllustrationPointCreateExtensionsTest.cs	(revision 0)
+++ Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/TopLevelSubMechanismIllustrationPointCreateExtensionsTest.cs	(revision ace63dd1e2a052cb8774347958f3f2e2013c7400)
@@ -0,0 +1,81 @@
+// Copyright (C) Stichting Deltares 2017. All rights reserved.
+//
+// This file is part of Ringtoets.
+//
+// Ringtoets is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+//
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using System;
+using System.Linq;
+using NUnit.Framework;
+using Application.Ringtoets.Storage.Create.IllustrationPoints;
+using Application.Ringtoets.Storage.DbContext;
+using Core.Common.TestUtil;
+using Ringtoets.Common.Data.IllustrationPoints;
+using Ringtoets.Common.Data.TestUtil;
+
+namespace Application.Ringtoets.Storage.Test.Create.IllustrationPoints
+{
+    [TestFixture]
+    public class TopLevelSubMechanismIllustrationPointCreateExtensionsTest
+    {
+        [Test]
+        public void Create_TopLevelSubMechanismIllustrationPointNull_ThrowsArgumentNullException()
+        {
+            // Call
+            TestDelegate call = () => ((TopLevelSubMechanismIllustrationPoint) null).Create(0);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("topLevelSubMechanismIllustrationPoint", exception.ParamName);
+        }
+
+        [Test]
+        public void Create_ValidTopLevelSubMechanismIllustrationPoint_ReturnsEntityWithSubMechanismIllustrationPointEntity()
+        {
+            // Setup
+            var random = new Random(21);
+            var illustrationPoint = new SubMechanismIllustrationPoint("Illustration point name",
+                                                                      random.NextDouble(),
+                                                                      Enumerable.Empty<SubMechanismIllustrationPointStochast>(),
+                                                                      Enumerable.Empty<IllustrationPointResult>());
+
+            var windDirection = new WindDirection("WindDirection Name", random.NextDouble());
+            var topLevelSubMechanismIllustrationPoint = new TopLevelSubMechanismIllustrationPoint(windDirection,
+                                                                                                  "Just a situation",
+                                                                                                  illustrationPoint);
+            int order = random.Next();
+
+            // Call
+            TopLevelSubMechanismIllustrationPointEntity entity =
+                topLevelSubMechanismIllustrationPoint.Create(order);
+
+            // Assert
+            TestHelper.AssertAreEqualButNotSame(topLevelSubMechanismIllustrationPoint.ClosingSituation, entity.ClosingSituation);
+            Assert.AreEqual(order, entity.Order);
+
+            TestHelper.AssertAreEqualButNotSame(windDirection.Name, entity.WindDirectionName);
+            Assert.AreEqual(windDirection.Angle, entity.WindDirectionAngle, windDirection.Angle.GetAccuracy());
+
+            SubMechanismIllustrationPointEntity subMechanismIllustrationPointEntity = entity.SubMechanismIllustrationPointEntity;
+            TestHelper.AssertAreEqualButNotSame(illustrationPoint.Name, subMechanismIllustrationPointEntity.Name);
+            Assert.AreEqual(illustrationPoint.Beta, subMechanismIllustrationPointEntity.Beta, illustrationPoint.Beta.GetAccuracy());
+            CollectionAssert.IsEmpty(subMechanismIllustrationPointEntity.IllustrationPointResultEntities);
+            CollectionAssert.IsEmpty(subMechanismIllustrationPointEntity.SubMechanismIllustrationPointStochastEntities);
+        }
+    }
+}
\ No newline at end of file
Fisheye: Tag ace63dd1e2a052cb8774347958f3f2e2013c7400 refers to a dead (removed) revision in file `Application/Ringtoets/test/Application.Ringtoets.Storage.Test/Create/IllustrationPoints/TopLevelSubMechanismIllustrationPointTest.cs'.
Fisheye: No comparison available.  Pass `N' to diff?