diff --git a/m-bptree.h b/m-bptree.h
index bfb3f452..da8270b3 100644
--- a/m-bptree.h
+++ b/m-bptree.h
@@ -82,7 +82,10 @@
 		      (__VA_ARGS__ )))
 
 /* Define the oplist of a rbtree of type (from BPTREE_DEF2).
-   USAGE: BPTREE_OPLIST2(name, key_oplist, value_oplist) */
+   USAGE: BPTREE_OPLIST2(name, key_oplist, value_oplist) 
+   NOTE: IT_REF is not exported so that the contained appears as not modifiable
+   by algorithm.
+*/
 #define BPTREE_OPLIST2(name, key_oplist, value_oplist)                  \
   (INIT(M_C(name, _init)),						\
    INIT_SET(M_C(name, _init_set)),					\
@@ -101,7 +104,6 @@
    IT_END_P(M_C(name,_end_p)),						\
    IT_EQUAL_P(M_C(name,_it_equal_p)),					\
    IT_NEXT(M_C(name,_next)),						\
-   IT_REF(M_C(name,_ref)),						\
    IT_CREF(M_C(name,_cref)),						\
    CLEAN(M_C(name,_clean)),						\
    GET_MIN(M_C(name,_min)),						\
diff --git a/m-dict.h b/m-dict.h
index 147f4075..19c975f1 100644
--- a/m-dict.h
+++ b/m-dict.h
@@ -917,7 +917,9 @@
    so that all arguments are evaluated before further expansion */
 #define DICTI_OPLIST_P1(arg) DICTI_OPLIST_P2 arg
 
-/* Define the oplist of a dictionnary */
+/* Define the oplist of a dictionnary
+   NOTE: IT_REF is not exported so that the contained appears as not modifiable
+   by algorithm.*/
 #define DICTI_OPLIST_P2(name, key_oplist, value_oplist)			\
   (INIT(M_C(name, _init)),						\
    INIT_SET(M_C(name, _init_set)),					\
@@ -938,7 +940,6 @@
    IT_END_P(M_C(name,_end_p)),						\
    IT_LAST_P(M_C(name,_last_p)),					\
    IT_NEXT(M_C(name,_next)),						\
-   IT_REF(M_C(name,_ref)),						\
    IT_CREF(M_C(name,_cref))						\
    ,KEY_TYPE(M_C(name, _key_type_t))                                    \
    ,VALUE_TYPE(M_C(name, _value_type_t))                                \
diff --git a/m-rbtree.h b/m-rbtree.h
index 2676626a..9848646d 100644
--- a/m-rbtree.h
+++ b/m-rbtree.h
@@ -50,7 +50,9 @@
    so that all arguments are evaluated before further expansion */
 #define RBTREEI_OPLIST_P1(arg) RBTREEI_OPLIST_P2 arg
 
-/* OPLIST definition of a rbtree */
+/* OPLIST definition of a rbtree
+   NOTE: IT_REF is not exported so that the contained appears as not modifiable
+   by algorithm.*/
 #define RBTREEI_OPLIST_P2(name, oplist)                                 \
   (INIT(M_C(name, _init)),						\
    INIT_SET(M_C(name, _init_set)),					\
@@ -73,7 +75,6 @@
    IT_LAST_P(M_C(name,_last_p)),					\
    IT_EQUAL_P(M_C(name,_it_equal_p)),					\
    IT_NEXT(M_C(name,_next)),						\
-   IT_REF(M_C(name,_ref)),						\
    IT_CREF(M_C(name,_cref)),						\
    CLEAN(M_C(name,_clean)),						\
    PUSH(M_C(name,_push)),						\