diff --git a/draw.cpp b/draw.cpp
index 1ae0eb6..fc349fa 100644
--- a/draw.cpp
+++ b/draw.cpp
@@ -1026,7 +1026,7 @@ void GraphicsWindow::Paint(int w, int h) {
     // And the naked edges, if the user did Analyze -> Show Naked Edges.
     glLineWidth(7);
     glColor3d(1, 0, 0);
-    glxDrawEdges(&(SS.nakedEdges));
+    glxDrawEdges(&(SS.nakedEdges), true);
 
     // Then redraw whatever the mouse is hovering over, highlighted.
     glDisable(GL_DEPTH_TEST); 
diff --git a/export.cpp b/export.cpp
index f68f111..f29b9cc 100644
--- a/export.cpp
+++ b/export.cpp
@@ -7,7 +7,7 @@ void SolveSpace::ExportSectionTo(char *filename) {
 
     Group *g = SK.GetGroup(SS.GW.activeGroup);
     g->GenerateDisplayItems();
-    if(g->displayMesh.l.n == 0) {
+    if(g->displayMesh.IsEmpty()) {
         Error("No solid model present; draw one with extrudes and revolves, "
               "or use Export 2d View to export bare lines and curves.");
         return;
@@ -100,7 +100,7 @@ void SolveSpace::ExportViewTo(char *filename) {
         g->GenerateDisplayItems();
         sm = &(g->displayMesh);
     }
-    if(sm->l.n == 0) {
+    if(sm->IsEmpty()) {
         sm = NULL;
     }
 
@@ -979,7 +979,7 @@ void HpglFileWriter::FinishAndCloseFile(void) {
 //-----------------------------------------------------------------------------
 void SolveSpace::ExportMeshTo(char *filename) {
     SMesh *m = &(SK.GetGroup(SS.GW.activeGroup)->displayMesh);
-    if(m->l.n == 0) {
+    if(m->IsEmpty()) {
         Error("Active group mesh is empty; nothing to export.");
         return;
     }
diff --git a/glhelper.cpp b/glhelper.cpp
index 8f5f93d..82a5c13 100644
--- a/glhelper.cpp
+++ b/glhelper.cpp
@@ -293,7 +293,7 @@ void glxDebugPolygon(SPolygon *p)
     }
 }
 
-void glxDrawEdges(SEdgeList *el)
+void glxDrawEdges(SEdgeList *el, bool endpointsToo)
 {
     SEdge *se;
     glBegin(GL_LINES);
@@ -302,13 +302,16 @@ void glxDrawEdges(SEdgeList *el)
         glxVertex3v(se->b);
     }
     glEnd();
-    glPointSize(12);
-    glBegin(GL_POINTS);
-    for(se = el->l.First(); se; se = el->l.NextAfter(se)) {
-        glxVertex3v(se->a);
-        glxVertex3v(se->b);
+
+    if(endpointsToo) {
+        glPointSize(12);
+        glBegin(GL_POINTS);
+        for(se = el->l.First(); se; se = el->l.NextAfter(se)) {
+            glxVertex3v(se->a);
+            glxVertex3v(se->b);
+        }
+        glEnd();
     }
-    glEnd();
 }
 
 void glxDebugMesh(SMesh *m)
diff --git a/groupmesh.cpp b/groupmesh.cpp
index e51c39d..4492800 100644
--- a/groupmesh.cpp
+++ b/groupmesh.cpp
@@ -51,15 +51,35 @@ void Group::GenerateLoops(void) {
     }
 }
 
-void Group::GenerateShellForStepAndRepeat(void) {
-    Group *src = SK.GetGroup(opA);
-    SShell *srcs = &(src->thisShell); // the shell to step and repeat
+void SShell::RemapFaces(Group *g, int remap) {
+    SSurface *ss;
+    for(ss = surface.First(); ss; ss = surface.NextAfter(ss)){
+        hEntity face = { ss->face };
+        if(face.v == Entity::NO_ENTITY.v) continue;
 
-    SShell workA, workB;
+        face = g->Remap(face, remap);
+        ss->face = face.v;
+    }
+}
+
+void SMesh::RemapFaces(Group *g, int remap) {
+    STriangle *tr;
+    for(tr = l.First(); tr; tr = l.NextAfter(tr)) {
+        hEntity face = { tr->meta.face };
+        if(face.v == Entity::NO_ENTITY.v) continue;
+
+        face = g->Remap(face, remap);
+        tr->meta.face = face.v;
+    }
+}
+
+template<class T>
+void Group::GenerateForStepAndRepeat(T *prevs, T *steps, T *outs, int how) {
+    T workA, workB;
     ZERO(&workA);
     ZERO(&workB);
-    SShell *soFar = &workA, *scratch = &workB;
-    soFar->MakeFromCopyOf(&(src->PreviousGroup()->runningShell));
+    T *soFar = &workA, *scratch = &workB;
+    soFar->MakeFromCopyOf(prevs);
 
     int n = (int)valA, a0 = 0;
     if(subtype == ONE_SIDED && skipFirst) {
@@ -70,13 +90,12 @@ void Group::GenerateShellForStepAndRepeat(void) {
         int ap = a*2 - (subtype == ONE_SIDED ? 0 : (n-1));
         int remap = (a == (n - 1)) ? REMAP_LAST : a;
 
-        SShell transd;
+        T transd;
         ZERO(&transd);
         if(type == TRANSLATE) {
             Vector trans = Vector::From(h.param(0), h.param(1), h.param(2));
             trans = trans.ScaledBy(ap);
-            Quaternion q = Quaternion::From(1, 0, 0, 0);
-            transd.MakeFromTransformationOf(srcs, trans, q);
+            transd.MakeFromTransformationOf(steps, trans, Quaternion::IDENTITY);
         } else {
             Vector trans = Vector::From(h.param(0), h.param(1), h.param(2));
             double theta = ap * SK.GetParam(h.param(3))->val;
@@ -84,43 +103,88 @@ void Group::GenerateShellForStepAndRepeat(void) {
             Vector axis = Vector::From(h.param(4), h.param(5), h.param(6));
             Quaternion q = Quaternion::From(c, s*axis.x, s*axis.y, s*axis.z);
             // Rotation is centered at t; so A(x - t) + t = Ax + (t - At)
-            transd.MakeFromTransformationOf(srcs,
+            transd.MakeFromTransformationOf(steps,
                 trans.Minus(q.Rotate(trans)), q);
         }
 
         // We need to rewrite any plane face entities to the transformed ones.
-        SSurface *ss;
-        for(ss = transd.surface.First(); ss; ss = transd.surface.NextAfter(ss)){
-            hEntity face = { ss->face };
-            if(face.v == Entity::NO_ENTITY.v) continue;
+        transd.RemapFaces(this, remap);
 
-            face = Remap(face, remap);
-            ss->face = face.v;
-        }
-
-        if(src->meshCombine == COMBINE_AS_DIFFERENCE) {
+        if(how == COMBINE_AS_DIFFERENCE) {
             scratch->MakeFromDifferenceOf(soFar, &transd);
-        } else if(src->meshCombine == COMBINE_AS_UNION) {
+        } else if(how == COMBINE_AS_UNION) {
             scratch->MakeFromUnionOf(soFar, &transd);
         } else {
             scratch->MakeFromAssemblyOf(soFar, &transd);
         }
-        SWAP(SShell *, scratch, soFar);
+        SWAP(T *, scratch, soFar);
 
         scratch->Clear();
         transd.Clear();
     }
 
-    runningShell.Clear();
-    runningShell = *soFar;
+    outs->Clear();
+    *outs = *soFar;
+}
+
+template<class T>
+void Group::GenerateForBoolean(T *prevs, T *thiss, T *outs) {
+    // If this group contributes no new mesh, then our running mesh is the
+    // same as last time, no combining required. Likewise if we have a mesh
+    // but it's suppressed.
+    if(thiss->IsEmpty() || suppress) {
+        outs->MakeFromCopyOf(prevs);
+        return;
+    }
+
+    // So our group's shell appears in thisShell. Combine this with the
+    // previous group's shell, using the requested operation.
+    if(meshCombine == COMBINE_AS_UNION) {
+        outs->MakeFromUnionOf(prevs, thiss);
+    } else if(meshCombine == COMBINE_AS_DIFFERENCE) {
+        outs->MakeFromDifferenceOf(prevs, thiss);
+    } else {
+        outs->MakeFromAssemblyOf(prevs, thiss);
+    }
 }
 
 void Group::GenerateShellAndMesh(void) {
     thisShell.Clear();
+    thisMesh.Clear();
+    runningShell.Clear();
+    runningMesh.Clear();
 
     if(type == TRANSLATE || type == ROTATE) {
-        GenerateShellForStepAndRepeat();
-        goto done;
+        Group *src = SK.GetGroup(opA);
+        Group *pg = src->PreviousGroup();
+
+        if(src->thisMesh.IsEmpty() && pg->runningMesh.IsEmpty() && !forceToMesh)
+        {
+            SShell *toStep = &(src->thisShell),
+                   *prev   = &(pg->runningShell);
+
+            GenerateForStepAndRepeat<SShell>
+                (prev, toStep, &runningShell, src->meshCombine);
+        } else {
+            SMesh prevm, stepm;
+            ZERO(&prevm);
+            ZERO(&stepm);
+
+            prevm.MakeFromCopyOf(&(pg->runningMesh));
+            pg->runningShell.TriangulateInto(&prevm);
+
+            stepm.MakeFromCopyOf(&(src->thisMesh));
+            src->thisShell.TriangulateInto(&stepm);
+
+            GenerateForStepAndRepeat<SMesh>
+                (&prevm, &stepm, &runningMesh, src->meshCombine);
+
+            stepm.Clear();
+            prevm.Clear();
+        }
+
+        displayDirty = true;
+        return;
     }
 
     if(type == EXTRUDE) {
@@ -205,51 +269,38 @@ void Group::GenerateShellAndMesh(void) {
             SK.GetParam(h.param(5))->val,
             SK.GetParam(h.param(6))->val };
 
-        for(int i = 0; i < impMesh.l.n; i++) {
-            STriangle st = impMesh.l.elem[i];
-
-            if(st.meta.face != 0) {
-                hEntity he = { st.meta.face };
-                st.meta.face = Remap(he, 0).v;
-            }
-            st.a = q.Rotate(st.a).Plus(offset);
-            st.b = q.Rotate(st.b).Plus(offset);
-            st.c = q.Rotate(st.c).Plus(offset);
-        }
+        thisMesh.MakeFromTransformationOf(&impMesh, offset, q);
+        thisMesh.RemapFaces(this, 0);
 
         thisShell.MakeFromTransformationOf(&impShell, offset, q);
-        SSurface *srf;
-        IdList<SSurface,hSSurface> *sl = &(thisShell.surface);
-        for(srf = sl->First(); srf; srf = sl->NextAfter(srf)) {
-            if(srf->face != 0) {
-                hEntity he = { srf->face };
-                srf->face = Remap(he, 0).v;
-            }
-        }
+        thisShell.RemapFaces(this, 0);
     }
 
-    runningShell.Clear();
+    // So now we've got the mesh or shell for this group. Combine it with
+    // the previous group's mesh or shell with the requested Boolean, and
+    // we're done.
 
-    // If this group contributes no new mesh, then our running mesh is the
-    // same as last time, no combining required. Likewise if we have a mesh
-    // but it's suppressed.
-    if(suppress) {
-        runningShell.MakeFromCopyOf(&(PreviousGroup()->runningShell));
-        goto done;
-    }
-
-    // So our group's shell appears in thisShell. Combine this with the
-    // previous group's shell, using the requested operation.
-    SShell *a = &(PreviousGroup()->runningShell);
-    if(meshCombine == COMBINE_AS_UNION) {
-        runningShell.MakeFromUnionOf(a, &thisShell);
-    } else if(meshCombine == COMBINE_AS_DIFFERENCE) {
-        runningShell.MakeFromDifferenceOf(a, &thisShell);
+    Group *pg = PreviousGroup();
+    if(pg->runningMesh.IsEmpty() && thisMesh.IsEmpty() && !forceToMesh) {
+        SShell *prevs = &(pg->runningShell);
+        GenerateForBoolean<SShell>(prevs, &thisShell, &runningShell);
     } else {
-        runningShell.MakeFromAssemblyOf(a, &thisShell);
+        SMesh prevm, thism;
+        ZERO(&prevm);
+        ZERO(&thism);
+
+        prevm.MakeFromCopyOf(&(pg->runningMesh));
+        pg->runningShell.TriangulateInto(&prevm);
+
+        thism.MakeFromCopyOf(&thisMesh);
+        thisShell.TriangulateInto(&thism);
+
+        GenerateForBoolean<SMesh>(&prevm, &thism, &runningMesh);
+
+        thism.Clear();
+        prevm.Clear();
     }
 
-done:
     displayDirty = true;
 }
 
@@ -257,8 +308,19 @@ void Group::GenerateDisplayItems(void) {
     if(displayDirty) {
         displayMesh.Clear();
         runningShell.TriangulateInto(&displayMesh);
+        STriangle *tr;
+        for(tr = runningMesh.l.First(); tr; tr = runningMesh.l.NextAfter(tr)) {
+            STriangle trn = *tr;
+            Vector n = trn.Normal();
+            trn.an = n;
+            trn.bn = n;
+            trn.cn = n;
+            displayMesh.AddTriangle(&trn);
+        }
+
         displayEdges.Clear();
         runningShell.MakeEdgesInto(&displayEdges);
+
         displayDirty = false;
     }
 }
@@ -314,7 +376,7 @@ void Group::Draw(void) {
         glxColor3d(REDf  (SS.edgeColor),
                    GREENf(SS.edgeColor), 
                    BLUEf (SS.edgeColor));
-        glxDrawEdges(&displayEdges);
+        glxDrawEdges(&displayEdges, false);
     }
 
     if(SS.GW.showMesh) glxDebugMesh(&displayMesh);
diff --git a/mesh.cpp b/mesh.cpp
index e1380b4..787b972 100644
--- a/mesh.cpp
+++ b/mesh.cpp
@@ -206,7 +206,7 @@ void SMesh::AddAgainstBsp(SMesh *srcm, SBsp3 *bsp3) {
     }
 }
 
-void SMesh::MakeFromUnion(SMesh *a, SMesh *b) {
+void SMesh::MakeFromUnionOf(SMesh *a, SMesh *b) {
     SBsp3 *bspa = SBsp3::FromMesh(a);
     SBsp3 *bspb = SBsp3::FromMesh(b);
 
@@ -219,7 +219,7 @@ void SMesh::MakeFromUnion(SMesh *a, SMesh *b) {
     AddAgainstBsp(a, bspb);
 }
 
-void SMesh::MakeFromDifference(SMesh *a, SMesh *b) {
+void SMesh::MakeFromDifferenceOf(SMesh *a, SMesh *b) {
     SBsp3 *bspa = SBsp3::FromMesh(a);
     SBsp3 *bspb = SBsp3::FromMesh(b);
 
@@ -232,40 +232,33 @@ void SMesh::MakeFromDifference(SMesh *a, SMesh *b) {
     AddAgainstBsp(a, bspb);
 }
 
-bool SMesh::MakeFromInterferenceCheck(SMesh *srca, SMesh *srcb, SMesh *error) {
-    SBsp3 *bspa = SBsp3::FromMesh(srca);
-    SBsp3 *bspb = SBsp3::FromMesh(srcb);
-
-    error->Clear();
-    error->flipNormal = true;
-    error->keepCoplanar = false;
-
-    error->AddAgainstBsp(srcb, bspa);
-    error->AddAgainstBsp(srca, bspb);
-    // Now we have a list of all the triangles (or fragments thereof) from
-    // A that lie inside B, or vice versa. That's the interference, and
-    // we report it so that it can be flagged.
-
-    // For the actual output, take the union.
-    flipNormal = false;
-    keepCoplanar = false;
-    AddAgainstBsp(srcb, bspa);
-
-    flipNormal = false;
-    keepCoplanar = true;
-    AddAgainstBsp(srca, bspb);
-    
-    // And we're successful if the intersection was empty.
-    return (error->l.n == 0);
-}
-
-void SMesh::MakeFromCopy(SMesh *a) {
+void SMesh::MakeFromCopyOf(SMesh *a) {
     int i;
     for(i = 0; i < a->l.n; i++) {
         AddTriangle(&(a->l.elem[i]));
     }
 }
 
+void SMesh::MakeFromAssemblyOf(SMesh *a, SMesh *b) {
+    MakeFromCopyOf(a);
+    MakeFromCopyOf(b);
+}
+
+void SMesh::MakeFromTransformationOf(SMesh *a, Vector trans, Quaternion q) {
+    STriangle *tr;
+    for(tr = a->l.First(); tr; tr = a->l.NextAfter(tr)) {
+        STriangle tt = *tr;
+        tt.a = (q.Rotate(tt.a)).Plus(trans);
+        tt.b = (q.Rotate(tt.b)).Plus(trans);
+        tt.c = (q.Rotate(tt.c)).Plus(trans);
+        AddTriangle(&tt);
+    }
+}
+
+bool SMesh::IsEmpty(void) {
+    return (l.n == 0);
+}
+
 DWORD SMesh::FirstIntersectionWith(Point2d mp) {
     Vector p0 = Vector::From(mp.x, mp.y, 0);
     Vector gn = Vector::From(0, 0, 1);
diff --git a/polygon.h b/polygon.h
index 183edff..ff1a113 100644
--- a/polygon.h
+++ b/polygon.h
@@ -184,10 +184,15 @@ public:
     void Simplify(int start);
 
     void AddAgainstBsp(SMesh *srcm, SBsp3 *bsp3);
-    void MakeFromUnion(SMesh *a, SMesh *b);
-    void MakeFromDifference(SMesh *a, SMesh *b);
-    bool MakeFromInterferenceCheck(SMesh *srca, SMesh *srcb, SMesh *errorAt);
-    void MakeFromCopy(SMesh *a);
+    void MakeFromUnionOf(SMesh *a, SMesh *b);
+    void MakeFromDifferenceOf(SMesh *a, SMesh *b);
+
+    void MakeFromCopyOf(SMesh *a);
+    void MakeFromTransformationOf(SMesh *a, Vector trans, Quaternion q);
+    void MakeFromAssemblyOf(SMesh *a, SMesh *b);
+
+    bool IsEmpty(void);
+    void RemapFaces(Group *g, int remap);
 
     DWORD FirstIntersectionWith(Point2d mp);
 };
diff --git a/sketch.h b/sketch.h
index 88ff6a7..96fb9df 100644
--- a/sketch.h
+++ b/sketch.h
@@ -208,9 +208,10 @@ public:
     void GenerateLoops(void);
     // And the mesh stuff
     Group *PreviousGroup(void);
-    void GenerateShellForStepAndRepeat(void);
     void GenerateDisplayItems(void);
     void GenerateShellAndMesh(void);
+    template<class T> void GenerateForStepAndRepeat(T *a, T *b, T *o, int how);
+    template<class T> void GenerateForBoolean(T *a, T *b, T *o);
     void Draw(void);
 
     SPolygon GetPolygon(void);
diff --git a/solvespace.h b/solvespace.h
index e0a1fbb..8a60a79 100644
--- a/solvespace.h
+++ b/solvespace.h
@@ -149,7 +149,7 @@ void vl(void); // debug function to validate heaps
 // End of platform-specific functions
 //================
 
-
+class Group;
 class SSurface;
 #include "dsc.h"
 #include "polygon.h"
@@ -175,7 +175,7 @@ void glxTesselatePolygon(GLUtesselator *gt, SPolygon *p);
 void glxFillPolygon(SPolygon *p);
 void glxFillMesh(int color, SMesh *m, DWORD h, DWORD s1, DWORD s2);
 void glxDebugPolygon(SPolygon *p);
-void glxDrawEdges(SEdgeList *l);
+void glxDrawEdges(SEdgeList *l, bool endpointsToo);
 void glxDebugMesh(SMesh *m);
 void glxMarkPolygonNormal(SPolygon *p);
 void glxWriteText(char *str);
diff --git a/srf/surface.cpp b/srf/surface.cpp
index 0ffcc63..3b685c2 100644
--- a/srf/surface.cpp
+++ b/srf/surface.cpp
@@ -666,6 +666,10 @@ void SShell::TriangulateInto(SMesh *sm) {
     }
 }
 
+bool SShell::IsEmpty(void) {
+    return (surface.n == 0);
+}
+
 void SShell::Clear(void) {
     SSurface *s;
     for(s = surface.First(); s; s = surface.NextAfter(s)) {
diff --git a/srf/surface.h b/srf/surface.h
index 33ddf86..25492df 100644
--- a/srf/surface.h
+++ b/srf/surface.h
@@ -319,6 +319,8 @@ public:
     void MakeEdgesInto(SEdgeList *sel);
     void MakeSectionEdgesInto(Vector n, double d,
                                 SEdgeList *sel, SBezierList *sbl);
+    bool IsEmpty(void);
+    void RemapFaces(Group *g, int remap);
     void Clear(void);
 };
 
diff --git a/textscreens.cpp b/textscreens.cpp
index 2144b3f..0b4a317 100644
--- a/textscreens.cpp
+++ b/textscreens.cpp
@@ -463,7 +463,7 @@ void TextWindow::ShowGroupInfo(void) {
              g->runningShell.surface.n > 0))
     {
         Group *pg = g->PreviousGroup();
-        if(pg->runningMesh.l.n == 0 && g->thisMesh.l.n == 0) {
+        if(pg->runningMesh.IsEmpty() && g->thisMesh.IsEmpty()) {
             bool fm = g->forceToMesh;
             Printf(true,
                 "%FtSURFACES%E %Fh%f%Ll%s%E%Fs%s%E / %Fh%f%Ll%s%E%Fs%s%E",
@@ -473,7 +473,7 @@ void TextWindow::ShowGroupInfo(void) {
                     (fm ? "" : "as mesh"), (fm ? "as mesh" : ""));
         } else {
             Printf(false,
-                "%FtSURFACES%E %Fas mesh%FE");
+                "%FtSURFACES%E %Fsas mesh%E");
         }
     }