diff --git a/src/engine/qofinstance.c b/src/engine/qofinstance.c
index 9e13cd01cf..c75122ddc7 100644
--- a/src/engine/qofinstance.c
+++ b/src/engine/qofinstance.c
@@ -1,12 +1,34 @@
+/********************************************************************\
+ * qofinstance.c -- handler for fields common to all objects        *
+ *                                                                  *
+ * This program 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 2 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, contact:                        *
+ *                                                                  *
+ * Free Software Foundation           Voice:  +1-617-542-5942       *
+ * 59 Temple Place - Suite 330        Fax:    +1-617-542-2652       *
+ * Boston, MA  02111-1307,  USA       gnu@gnu.org                   *
+ *                                                                  *
+\********************************************************************/
+
 /*
- * qofinstance.c
- *
  * Object instance holds many common fields that most
  * gnucash objects use.
  * 
  * Copyright (C) 2003 Linas Vepstas <linas@linas.org>
  */
 
+#include "gnc-trace.h"
+
 #include "kvp-util-p.h"
 #include "qofbook.h"
 #include "qofbook-p.h"
@@ -14,6 +36,10 @@
 #include "qofid-p.h"
 #include "qofinstance.h"
 
+static short module = MOD_ENGINE;
+
+/* ========================================================== */
+
 void 
 qof_instance_init (QofInstance *inst, QofBook *book)
 {
@@ -53,6 +79,8 @@ qof_instance_get_slots (QofInstance *inst)
   return inst->kvp_data;
 }
 
+/* ========================================================== */
+
 void
 qof_instance_gemini (QofInstance *to, QofInstance *from)
 {
@@ -72,3 +100,31 @@ qof_instance_gemini (QofInstance *to, QofInstance *from)
   to->dirty = TRUE;
 }
 
+QofInstance *
+qof_instance_lookup_twin (QofInstance *src, QofBook *target_book)
+{
+   QofEntityTable *src_etable, *target_etable;
+   QofIdType etype;
+   KvpFrame *fr;
+   GUID * twin_guid;
+   QofInstance * twin;
+                                                                                
+   if (!src || !target_book) return NULL;
+   ENTER (" ");
+
+   fr = gnc_kvp_bag_find_by_guid (src->kvp_data, "gemini",
+                    "book_guid", &src->guid);
+                                                                                
+   twin_guid = kvp_frame_get_guid (fr, "inst_guid");
+
+   src_etable = qof_book_get_entity_table (src->book);
+   etype = qof_entity_type (src_etable, &src->guid);
+
+   target_etable = qof_book_get_entity_table (target_book);
+   twin = qof_entity_lookup (target_etable, twin_guid, etype);
+
+   LEAVE (" found twin=%p", twin);
+   return twin;
+}
+
+/* ========================== END OF FILE ======================= */
diff --git a/src/engine/qofinstance.h b/src/engine/qofinstance.h
index 3109e7730d..32a31e576d 100644
--- a/src/engine/qofinstance.h
+++ b/src/engine/qofinstance.h
@@ -1,6 +1,25 @@
+/********************************************************************\
+ * qofinstance.h -- fields common to all object instances           *
+ *                                                                  *
+ * This program 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 2 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, contact:                        *
+ *                                                                  *
+ * Free Software Foundation           Voice:  +1-617-542-5942       *
+ * 59 Temple Place - Suite 330        Fax:    +1-617-542-2652       *
+ * Boston, MA  02111-1307,  USA       gnu@gnu.org                   *
+ *                                                                  *
+\********************************************************************/
 /*
- * qofinstance.h
- *
  * Object instance holds many common fields that most
  * gnucash objects use.
  * 
@@ -29,12 +48,26 @@ struct QofInstance_s
  * eventually, it may hold more fields, such as refrence counting...
  *
  */
+
+   /* Globally unique account id identifying this instance */
    GUID guid;
+
+   /* The entity_table in which this instance is stored */
    QofBook * book;
+
+  /* kvp_data is a key-value pair database for storing arbirtary
+   * information associated with this instance.  
+   * See src/engine/kvp_doc.txt for a list and description of the 
+   * important keys. */
    KvpFrame *kvp_data;
 
+   /* Keep track of nesting level of begin/end edit calls */
    int    editlevel;
+
+   /* In process of being destroyed */
    gboolean  do_free;
+
+   /* This instance has not been saved yet */
    gboolean  dirty;
 };
 
@@ -60,4 +93,7 @@ KvpFrame* qof_instance_get_slots (QofInstance *);
  */
 void qof_instance_gemini (QofInstance *to, QofInstance *from);
 
+/** Look up the gemini'ed twin to 'src' in the book 'book'. */
+QofInstance * qof_instance_lookup_twin (QofInstance *src, QofBook *book);
+
 #endif /* QOF_INSTANCE_H */