diff --git a/api/Makefile.am b/api/Makefile.am
index 059d355ee7..5483be7894 100644
--- a/api/Makefile.am
+++ b/api/Makefile.am
@@ -6,10 +6,12 @@ include $(top_srcdir)/Makefile.incl
 AM_CFLAGS += @GLUT_CFLAGS@
 AM_LDFLAGS += @GLUT_LIBS@
 
+# stuff linked into both main app and graphics app
 api_files= \
 	boinc_api.C \
     graphics2_util.C
 
+# stuff linked into graphics app
 graphics2_files = \
 	gutil.C	            \
 	gutil_text.C	    \
@@ -21,8 +23,8 @@ graphics2_files = \
     graphics2_unix.C
 
 if OS_DARWIN
-	api_files += mac_icon.C
-	graphics2_files += macglutfix.m
+    graphics2_files += mac_icon.C
+    graphics2_files += macglutfix.m
 endif
 
 EXTRA_DIST = *.h
diff --git a/api/graphics2.C b/api/graphics2.C
index 00f55ce129..7c069c88a9 100644
--- a/api/graphics2.C
+++ b/api/graphics2.C
@@ -1,3 +1,24 @@
+// Berkeley Open Infrastructure for Network Computing
+// http://boinc.berkeley.edu
+// Copyright (C) 2008 University of California
+//
+// This is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation;
+// either version 2.1 of the License, or (at your option) any later version.
+//
+// This software 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 Lesser General Public License for more details.
+//
+// To view the GNU Lesser General Public License visit
+// http://www.gnu.org/copyleft/lesser.html
+// or write to the Free Software Foundation, Inc.,
+// 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+// platform-independent part of graphics library
+//
 #include "util.h"
 #include "app_ipc.h"
 #include "shmem.h"
diff --git a/api/graphics2_unix.C b/api/graphics2_unix.C
index dbb99dbdac..f8b66706eb 100644
--- a/api/graphics2_unix.C
+++ b/api/graphics2_unix.C
@@ -1,3 +1,24 @@
+// Berkeley Open Infrastructure for Network Computing
+// http://boinc.berkeley.edu
+// Copyright (C) 2008 University of California
+//
+// This is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation;
+// either version 2.1 of the License, or (at your option) any later version.
+//
+// This software 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 Lesser General Public License for more details.
+//
+// To view the GNU Lesser General Public License visit
+// http://www.gnu.org/copyleft/lesser.html
+// or write to the Free Software Foundation, Inc.,
+// 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+// unix-specific graphics stuff
+//
 #include "config.h"
 #include <stdlib.h>
 #include <stdio.h>    
diff --git a/api/graphics2_util.C b/api/graphics2_util.C
index d4f0128d29..bde2658f38 100644
--- a/api/graphics2_util.C
+++ b/api/graphics2_util.C
@@ -1,3 +1,25 @@
+// Berkeley Open Infrastructure for Network Computing
+// http://boinc.berkeley.edu
+// Copyright (C) 2008 University of California
+//
+// This is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation;
+// either version 2.1 of the License, or (at your option) any later version.
+//
+// This software 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 Lesser General Public License for more details.
+//
+// To view the GNU Lesser General Public License visit
+// http://www.gnu.org/copyleft/lesser.html
+// or write to the Free Software Foundation, Inc.,
+// 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+// graphics-related utilities, used both from main applications
+// (set create shared mem) and by the graphics app
+
 #ifdef _WIN32
 #include "boinc_win.h"
 #elif (!defined(__EMX__))
diff --git a/api/graphics2_win.C b/api/graphics2_win.C
index cd90d81c7f..35afbea86d 100644
--- a/api/graphics2_win.C
+++ b/api/graphics2_win.C
@@ -375,18 +375,18 @@ void boinc_graphics_loop(int argc, char** argv) {
 
 extern int main(int, char**);
 
-static HINSTANCE hInstance = NULL;
+static HINSTANCE instance = NULL;
 
 // call this with the resource names you compiled the icons with
 // (16x16 and 48x48 pixel)
 //
-void boinc_set_windows_icon(const char*icon16,const char*icon48) {
+void boinc_set_windows_icon(const char* icon16, const char* icon48) {
     LONG ic;
     HWND hWnd=FindWindow("BOINC_app",NULL);
-    if (ic=(LONG)LoadIcon(hInstance,icon48)) {
+    if (ic=(LONG)LoadIcon(instance,icon48)) {
         SetClassLongPtr(hWnd,GCLP_HICON,ic);
     }
-    if (ic=(LONG)LoadImage(hInstance,icon16, IMAGE_ICON, 16, 16, 0)) {
+    if (ic=(LONG)LoadImage(instance,icon16, IMAGE_ICON, 16, 16, 0)) {
         SetClassLongPtr(hWnd,GCLP_HICONSM,ic);
     }
 }
@@ -396,7 +396,7 @@ int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPrevInst, LPSTR Args, int WinMode
     char* argv[100];
     int argc;
 
-    hInstance = hInst;
+    instance = hInst;
     command_line = GetCommandLine();
     argc = parse_command_line(command_line, argv);
     main(argc, argv);
diff --git a/api/graphics_api.C b/api/graphics_api.C
index 3826131c05..7f0f819bbe 100644
--- a/api/graphics_api.C
+++ b/api/graphics_api.C
@@ -17,6 +17,8 @@
 // or write to the Free Software Foundation, Inc.,
 // 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 
+// DEPRECATED - DO NOT USE
+
 #if defined(_WIN32) && !defined(__STDWX_H__) && !defined(_BOINC_WIN_) && !defined(_AFX_STDAFX_H_)
 #include "boinc_win.h"
 #else
diff --git a/checkin_notes b/checkin_notes
index c218e7bbed..c1039dcf94 100644
--- a/checkin_notes
+++ b/checkin_notes
@@ -822,3 +822,16 @@ David  Jan 28 2008
         http_curl.C
         log_flags.C,h
         scheduler_op.C
+
+David  Jan 28 2008
+    - API: fix Win build error
+    - API: fix Makefile.am
+    - add LGPL license on some files
+
+    api/
+        Makefile.am
+        graphics_api.C
+        graphics2_win.C
+        graphics2_unix.C
+        graphics2_util.C
+        graphics2.C
diff --git a/db/bolt_schema.sql b/db/bolt_schema.sql
index 2fb869eae4..9a7316e97f 100644
--- a/db/bolt_schema.sql
+++ b/db/bolt_schema.sql
@@ -76,7 +76,7 @@ create table bolt_result (
 );
 
 -- represents the result of a completed exercise set,
--- where "completed" means the student clicked Next on the final answer page.
+-- where "completed" means the last exercise was scored.
 -- In theory this could be reconstructed from the individual exercise results,
 -- but this table makes it easier for analytics
 --
diff --git a/html/inc/bolt.inc b/html/inc/bolt.inc
index faf59e6a7e..8587524168 100644
--- a/html/inc/bolt.inc
+++ b/html/inc/bolt.inc
@@ -1,25 +1,11 @@
 <?php
 
+// Bolt course document API
+
 error_reporting(E_ALL);
 ini_set('display_errors', true);
 ini_set('display_startup_errors', true);
 
-// stuff needed in Bolt course documents
-
-// rules about course structures:
-//
-// - Each unit has a logical name.
-// - The members of a set must have distinct logical names
-// - Different units may have the same logical name;
-//   however, such units must be identical.
-
-// A state in a course is described by:
-// - an associative array mapping logical names to state structures.
-//   Typically this includes the logical name of the current child
-//   and info such as a sequence index.
-//   This is kind of like a "call stack",
-//   except that it can contain units not currently active.
-
 abstract class BoltUnit {
     public $name;   // logical name.
     public $title;
@@ -36,47 +22,8 @@ abstract class BoltUnit {
         // frac_done: Fraction done (of this unit and any subunits)
 }
 
-// An iterator represents a user's position in a course.
-// Its state is stored in the database,
-// and the course may change underneath it.
+// base class for exercise and lesson
 //
-class BoltIter {
-    public $top;        // topmost unit
-    public $state;
-    public $xset;       // exercise set, if any
-
-    // the following are temps
-    public $item;       // current item
-    public $frac_done;  // fraction done
-
-    function __construct($top) {
-        $this->top = $top;
-        $this->state = array();
-    }
-
-    function decode_state($encoded_state) {
-        $this->state = json_decode($encoded_state, true);
-    }
-
-    function encode_state() {
-        return json_encode($this->state);
-    }
-
-    // get current item and fraction done
-    //
-    function at() {
-        $this->xset = null;
-        $this->top->walk($this, false, $this->frac_done);
-    }
-
-    // move to the next item, and return it in $this->item
-    // (null if course finished)
-    //
-    function next() {
-        $this->top->walk($this, true, $this->frac_done);
-    }
-}
-
 class BoltItem extends BoltUnit {
     public $filename;
     public $query_string;
@@ -113,6 +60,106 @@ class BoltExercise extends BoltItem {
     }
 }
 
+// Base class for control structures (i.e. all units that are not items).
+// These have the following properties:
+// - a set of units
+// - an ordering of this set, defined in the derived class
+//   (i.e., random, student-specific, or identity)
+// - an index (state_rec::index) for where we are in this list
+// - an index (state_rec::nshown) for how many units completed so far
+// - a number "ntoshow" for how many to show
+//
+class BoltSet extends BoltUnit {
+    public $units;
+    function __construct($name, $units, $ntoshow) {
+        $this->name = $name;
+        $this->is_item = false;
+        $this->units = $units;
+        $this->ntoshow = $ntoshow;
+        $this->ordered = false;
+    }
+    function walk(&$iter, $incr, &$frac_done) {
+        $n = count($this->units);
+        if (array_key_exists($this->name, $iter->state)) {
+            $state_rec = $iter->state[$this->name];
+            $child_name = $state_rec['child_name'];
+            $nshown = $state_rec['nshown'];
+            if (!$this->ordered) {
+                $this->order($state_rec);
+                $this->ordered = true;
+            }
+
+            // look up unit by name
+            // 
+            $child = null;
+            for ($i=0; $i<$n; $i++) {
+                $c = $this->units[$i];
+                if ($c->name == $child_name) {
+                    $child = $c;
+                    break;
+                }
+            }
+
+            // if not there, look up by index
+            //
+            if (!$child) {
+                $i = $state_rec['index'];
+                if ($i >= $n) {
+                    // and if index is too big, use last unit
+                    //
+                    $i = $n-1;
+                }
+                $child = $this->units[$i];
+            }
+
+            // at this point, $child is the current unit, and $i is its index
+            //
+            if ($incr) {
+                if ($child->is_item) {
+                    $my_inc = true;
+                } else {
+                    $my_inc = $child->walk($iter, $incr, $frac_done);
+                }
+                if ($my_inc) {
+                    $nshown++;
+                    if ($nshown == $this->ntoshow) {
+                        $frac_done = 1;
+                        $state_rec['nshown'] = 0;
+                        $state_rec['child_name'] = null;
+                        $iter->state[$this->name] = $state_rec;
+                        return true;
+                    } else {
+                        $i = ($i+1)%$n;
+                    }
+                }
+            }
+        } else {
+            // here if no state record; initialize
+            //
+            $i = 0;
+            $nshown = 0;
+            $state_rec = null;
+            $this->order($state_rec);
+        }
+
+        // at this point, $i is index of current child
+        //
+        $child = $this->units[$i];
+        $frac_done = $nshown/$n;
+        $state_rec['index'] = $i;
+        $state_rec['nshown'] = $nshown;
+        $state_rec['child_name'] = $child->name;
+        $iter->state[$this->name] = $state_rec;
+        if ($child->is_item) {
+            $iter->item = $child;
+        } else {
+            $child->walk($iter, false, $f);
+            $frac_done += $f*(1/$n);
+        }
+        return false;
+    }
+}
+
 function name($n) {
     return array('name', $n);
 }
@@ -185,19 +232,6 @@ function exercise() {
     return new BoltExercise($name, $title, $file);
 }
 
-function enum_course($course) {
-    $iter = new BoltIter($course);
-    while (1) {
-        $x = $iter->at();
-        if (!$x) break;
-        echo "at: $x->url\n";
-        $x = $iter->next();
-        if (!$x) break;
-        echo "next: $x->filename\n";
-    }
-    echo "course over\n";
-}
-
 require_once('../inc/bolt_seq.inc');
 require_once('../inc/bolt_rnd.inc');
 require_once('../inc/bolt_xset.inc');
diff --git a/html/inc/bolt_ex.inc b/html/inc/bolt_ex.inc
index 4025ab1c4c..bb8212fd9b 100644
--- a/html/inc/bolt_ex.inc
+++ b/html/inc/bolt_ex.inc
@@ -1,5 +1,7 @@
 <?php
 
+// Bolt exercise API
+
 $bolt_ex_mode = 0;
 $bolt_ex_index = 0;
 $bolt_ex_state = 0;
diff --git a/html/inc/bolt_rnd.inc b/html/inc/bolt_rnd.inc
index fcdbb4f06b..502361eecb 100644
--- a/html/inc/bolt_rnd.inc
+++ b/html/inc/bolt_rnd.inc
@@ -1,99 +1,20 @@
 <?php
 
-// state for random unit is:
-// seed         The RNG seed used to shuffle
-// i            index of current child
-// number_shown number of units shown so far (not necessarily the
-//              same as i on 2nd and later pass through this unit)
-// child_name   name of current child
-class BoltRandom extends BoltUnit {
+class BoltRandom extends BoltSet {
     public $units;
     function __construct($name, $units, $number) {
-        $this->name = $name;
-        $this->units = $units;
-        $this->number = $number;
-        $this->is_item = false;
-        $this->shuffled = false;
+        parent::__construct($name, $units, $number);
     }
 
-    function walk(&$iter, $incr, &$frac_done) {
-        $n = count($this->units);
-        if (array_key_exists($this->name, $iter->state)) {
-            $state_rec = $iter->state[$this->name];
-            $child_name = $state_rec['child_name'];
-            $number_shown = $state_rec['number_shown'];
-            if (!$this->shuffled) {
-                srand($state_rec['seed']);
-                shuffle($this->units);
-                $this->shuffled = true;
-            }
-
-            // look up unit by name
-            // 
-            $child = null;
-            for ($i=0; $i<$n; $i++) {
-                $c = $this->units[$i];
-                if ($c->name == $child_name) {
-                    $child = $c;
-                    break;
-                }
-            }
-
-            // if not there, look up by index
-            //
-            if (!$child) {
-                $i = $state_rec['i'];
-                if ($i >= $n) {
-                    // and if index is too big, use last unit
-                    //
-                    $i = $n-1;
-                }
-                $child = $this->units[$i];
-            }
-
-            // at this point, $child is the current unit, and $i is its index
-            //
-            if ($incr) {
-                $my_inc = false;
-                if ($child->is_item) {
-                    $my_inc = true;
-                } else {
-                    $my_inc = $child->walk($iter, $incr, $frac_done);
-                }
-                if ($my_inc) {
-                    $i = ($i+1)%$n;
-                    $number_shown++;
-                    if ($number_shown >= $this->number) {
-                        $frac_done = 1;
-                        $state_rec['i'] = $i;
-                        $state_rec['number_shown'] = 0;
-                        $state_rec['child_name'] = null;
-                        $iter->state[$this->name] = $state_rec;
-                        return true;
-                    }
-                }
-            }
+    function order(&$state_rec) {
+        if ($state_rec) {
+            $seed = $state_rec['seed'];
         } else {
-            $i = 0;
-            $number_shown = 0;
-            $state_rec = null;
             $seed = ((double)microtime()*1000000);
-            srand($seed);
-            shuffle($this->units);
             $state_rec['seed'] = $seed;
         }
-        $child = $this->units[$i];
-        $frac_done = $number_shown/$this->number;
-        $state_rec['i'] = $i;
-        $state_rec['number_shown'] = $number_shown;
-        $state_rec['child_name'] = $child->name;
-        $iter->state[$this->name] = $state_rec;
-        if ($child->is_item) {
-            $iter->item = $child;
-        } else {
-            $child->walk($iter, false, $f);
-            $frac_done += $f*(1/$number);
-        }
+        srand($seed);
+        shuffle($this->units);
     }
 }
 
diff --git a/html/inc/bolt_sched.inc b/html/inc/bolt_sched.inc
new file mode 100644
index 0000000000..b1a1471b28
--- /dev/null
+++ b/html/inc/bolt_sched.inc
@@ -0,0 +1,65 @@
+<?php
+
+// An iterator represents a user's position in a course.
+// Its state is stored in the database,
+// and the course may change underneath it.
+//
+// A state in a course is described by:
+// - an associative array mapping logical names to state structures.
+//   Typically this includes the logical name of the current child
+//   and info such as a sequence index.
+//   This is kind of like a "call stack",
+//   except that it can contain units not currently active.
+
+//
+class BoltIter {
+    public $top;        // topmost unit
+    public $state;
+    public $xset;       // exercise set, if any
+
+    // the following are temps
+    public $item;       // current item
+    public $frac_done;  // fraction done
+
+    function __construct($top) {
+        $this->top = $top;
+        $this->state = array();
+    }
+
+    function decode_state($encoded_state) {
+        $this->state = json_decode($encoded_state, true);
+    }
+
+    function encode_state() {
+        return json_encode($this->state);
+    }
+
+    // get current item and fraction done
+    //
+    function at() {
+        $this->xset = null;
+        $this->top->walk($this, false, $this->frac_done);
+    }
+
+    // move to the next item, and return it in $this->item
+    // (null if course finished)
+    //
+    function next() {
+        $this->top->walk($this, true, $this->frac_done);
+    }
+}
+
+function enum_course($course) {
+    $iter = new BoltIter($course);
+    while (1) {
+        $x = $iter->at();
+        if (!$x) break;
+        echo "at: $x->url\n";
+        $x = $iter->next();
+        if (!$x) break;
+        echo "next: $x->filename\n";
+    }
+    echo "course over\n";
+}
+
+?>
diff --git a/html/inc/bolt_seq.inc b/html/inc/bolt_seq.inc
index 55f6d9fc59..31af6e007f 100644
--- a/html/inc/bolt_seq.inc
+++ b/html/inc/bolt_seq.inc
@@ -1,77 +1,11 @@
 <?php
 
-class BoltSequence extends BoltUnit {
-    public $units;
+class BoltSequence extends BoltSet {
     function __construct($name, $units) {
-        $this->name = $name;
-        $this->units = $units;
-        $this->is_item = false;
+        parent::__construct($name, $units, count($units));
     }
 
-    function walk(&$iter, $incr, &$frac_done) {
-        $n = count($this->units);
-        if (array_key_exists($this->name, $iter->state)) {
-            $state_rec = $iter->state[$this->name];
-            $child_name = $state_rec['child_name'];
-
-            // look up unit by name
-            // 
-            $child = null;
-            for ($i=0; $i<$n; $i++) {
-                $c = $this->units[$i];
-                if ($c->name == $child_name) {
-                    $child = $c;
-                    break;
-                }
-            }
-
-            // if not there, look up by index
-            //
-            if (!$child) {
-                $i = $state_rec['i'];
-                if ($i >= $n) {
-                    // and if index is too big, use last unit
-                    //
-                    $i = $n-1;
-                }
-                $child = $this->units[$i];
-            }
-
-            // at this point, $child is the current unit, and $i is its index
-            //
-            if ($incr) {
-                $my_inc = false;
-                if ($child->is_item) {
-                    $my_inc = true;
-                } else {
-                    $my_inc = $child->walk($iter, $incr, $frac_done);
-                }
-                if ($my_inc) {
-                    $i++;
-                    if ($i == $n) {
-                        $frac_done = 1;
-                        $state_rec['i'] = 0;
-                        $state_rec['child_name'] = null;
-                        $iter->state[$this->name] = $state_rec;
-                        return true;
-                    }
-                }
-            }
-        } else {
-            $i = 0;
-        }
-        $child = $this->units[$i];
-        $frac_done = $i/$n;
-        $state_rec = null;
-        $state_rec['i'] = $i;
-        $state_rec['child_name'] = $child->name;
-        $iter->state[$this->name] = $state_rec;
-        if ($child->is_item) {
-            $iter->item = $child;
-        } else {
-            $child->walk($iter, false, $f);
-            $frac_done += $f*(1/$n);
-        }
+    function order() {
     }
 }
 
diff --git a/html/inc/bolt_xset.inc b/html/inc/bolt_xset.inc
index 9d0282ba24..2df0566416 100644
--- a/html/inc/bolt_xset.inc
+++ b/html/inc/bolt_xset.inc
@@ -1,128 +1,48 @@
 <?php
 
-class BoltExerciseSet extends BoltUnit {
-    public $units;
+class BoltExerciseSet extends BoltRandom {
     public $repeats;
-    public $state_rec;
     function __construct($name, $units, $number, $repeats) {
-        $this->name = $name;
-        $this->units = $units;
-        $this->number = $number;
+        parent::__construct($name, $units, $number);
         $this->repeats = $repeats;
-        $this->is_item = false;
-        $this->shuffled = false;
     }
 
-    // the scheduler calls this when an exercise in this set
-    // has just been graded.
+    // called when an exercise in this set has just been graded.
     // - record the score in our state structure
     // - return a structure saying what navigation info to show:
     //   - review
     //   - repeat now
     //   - next
     //
-    function xset_callback($iter, $score, &$is_last, &$nav_info) {
+    function xset_callback(&$iter, $score, $view_id, &$is_last, &$nav_info) {
+        echo "XSET_CALLBACK: $score";
+        $nav_info = null;
         $state_rec = $iter->state[$this->name];
-        $number_shown = $state_rec['number_shown'];
-        $state_rec['scores'][$number_shown] = $score;
-        $is_last = ($number_shown == $this->number);
-        if ($is_last) {
-        } else {
-        }
-    }
+        $nshown = $state_rec['nshown'];
+        $state_rec['scores'][$nshown] = $score;
+        $iter->state[$this->name] = $state_rec;
+        $is_last = ($nshown == $this->ntoshow);
+        if (!$is_last) return;
+
+        // this exercise set is now "completed".
+        //   - create exercise_set_result record
+        //   - optionally create or update bolt_refresh record
+        //
+        $total_score = 0;
+        for ($i=0; $i<$nshown; $i++) {
+            $total_score += $state_rec['score'][$i];
+        }
+        $avg_score = $total_score/$nshown;
 
-    // The user clicked "Next" on last answer page,
-    // so this exercise set is now "completed".
-    //   - create exercise_set_result record
-    //   - optionally create or update bolt_refresh record
-    //
-    function completed($score, $view_id) {
         $now = time();
-        $id = BoincXsetResult::insert("(create_time, user_id, course_id, name, score, view_id) values ($now, $user->id, $course->id, '$this->name', $score, $view_id)");
+        $id = BoincXsetResult::insert("(create_time, user_id, course_id, name, score, view_id) values ($now, $user->id, $course->id, '$this->name', $avg_score, $view_id)");
         $due_time = $now + 100000;
         BoincRefresh::replace("create_time=$now, user_id=$user->id, course_id=$course->id, name='$this->name', set_result_id=$id, due_time=$due_time");
     }
 
     function walk(&$iter, $incr, &$frac_done) {
         $iter->xset = $this;
-        $n = count($this->units);
-        if (array_key_exists($this->name, $iter->state)) {
-            $state_rec = $iter->state[$this->name];
-            $this->state_rec = $state_rec;
-            $child_name = $state_rec['child_name'];
-            $number_shown = $state_rec['number_shown'];
-            if (!$this->shuffled) {
-                srand($state_rec['seed']);
-                shuffle($this->units);
-                $this->shuffled = true;
-            }
-
-            // look up unit by name
-            // 
-            $child = null;
-            for ($i=0; $i<$n; $i++) {
-                $c = $this->units[$i];
-                if ($c->name == $child_name) {
-                    $child = $c;
-                    break;
-                }
-            }
-
-            // if not there, look up by index
-            //
-            if (!$child) {
-                $i = $state_rec['i'];
-                if ($i >= $n) {
-                    // and if index is too big, use last unit
-                    //
-                    $i = $n-1;
-                }
-                $child = $this->units[$i];
-            }
-
-            // at this point, $child is the current unit, and $i is its index
-            //
-            if ($incr) {
-                $my_inc = false;
-                if ($child->is_item) {
-                    $my_inc = true;
-                } else {
-                    $my_inc = $child->walk($iter, $incr, $frac_done);
-                }
-                if ($my_inc) {
-                    $i = ($i+1)%$n;
-                    $number_shown++;
-                    if ($number_shown >= $this->number) {
-                        $frac_done = 1;
-                        $state_rec['i'] = $i;
-                        $state_rec['number_shown'] = 0;
-                        $state_rec['child_name'] = null;
-                        $iter->state[$this->name] = $state_rec;
-                        return true;
-                    }
-                }
-            }
-        } else {
-            $i = 0;
-            $number_shown = 0;
-            $state_rec = null;
-            $seed = ((double)microtime()*1000000);
-            srand($seed);
-            shuffle($this->units);
-            $state_rec['seed'] = $seed;
-        }
-        $child = $this->units[$i];
-        $frac_done = $number_shown/$this->number;
-        $state_rec['i'] = $i;
-        $state_rec['number_shown'] = $number_shown;
-        $state_rec['child_name'] = $child->name;
-        $iter->state[$this->name] = $state_rec;
-        if ($child->is_item) {
-            $iter->item = $child;
-        } else {
-            $child->walk($iter, false, $f);
-            $frac_done += $f*(1/$number);
-        }
+        return parent::walk($iter, $incr, $frac_done);
     }
 }
 
diff --git a/html/user/bolt_sched.php b/html/user/bolt_sched.php
index e687024764..2cd3b53aa9 100644
--- a/html/user/bolt_sched.php
+++ b/html/user/bolt_sched.php
@@ -6,6 +6,7 @@
 //   action: see commands below
 
 require_once("../inc/bolt.inc");
+require_once("../inc/bolt_sched.inc");
 require_once("../inc/bolt_db.inc");
 require_once("../inc/bolt_ex.inc");
 require_once("../inc/bolt_util.inc");
@@ -261,11 +262,11 @@ case 'next':            // "next" button in lesson or exercise answer page
     break;
 case 'answer':          // submit answer in exercise
     $view = finalize_view($user, $view_id, BOLT_ACTION_SUBMIT);
-    if ($user->bolt->debug) {
-        echo "<pre>State: $view->state</pre>\n";
-    }
     $iter = new BoltIter($course_doc);
     $iter->decode_state($view->state);
+    if ($user->bolt->debug) {
+        echo "<pre>Initial state:"; print_r($iter->state); echo "</pre>\n";
+    }
     $iter->at();
 
     if ($user->bolt->debug) {
@@ -303,6 +304,12 @@ case 'answer':          // submit answer in exercise
     );
     $view->update("result_id=$result_id");
 
+    // If this is part of an exercise set, call its callback function
+    //
+    if ($iter->xset) {
+        $iter->xset->xset_callback($iter, $bolt_ex_score, $view->id, $is_last, $nav_info);
+    }
+
     // show the answer page
 
     srand($view_id);