diff --git a/lib/chibi/iset.sld b/lib/chibi/iset.sld
index 45462add..eb7e4763 100644
--- a/lib/chibi/iset.sld
+++ b/lib/chibi/iset.sld
@@ -73,5 +73,5 @@
    iset-union iset-union! iset-intersection iset-intersection!
    iset-difference iset-difference!
    iset-empty? iset-fold iset-fold-node iset-for-each iset-for-each-node
-   iset-map iset->list iset-size
+   iset-map iset->list iset-size iset= iset<= iset>=
    iset-cursor iset-cursor? iset-cursor-next iset-ref end-of-iset?))
diff --git a/lib/chibi/iset/constructors.scm b/lib/chibi/iset/constructors.scm
index d8865ed0..bdbc4e3b 100644
--- a/lib/chibi/iset/constructors.scm
+++ b/lib/chibi/iset/constructors.scm
@@ -35,11 +35,6 @@
 (define (iset-copy-node iset)
   (%make-iset (iset-start iset) (iset-end iset) (iset-bits iset) #f #f))
 
-(define (iset-set-node! a b)
-  (iset-start-set! a (iset-start b))
-  (iset-end-set! a (iset-end b))
-  (iset-bits-set! a (iset-bits b)))
-
 (define (iset-max-end iset)
   (cond ((iset-right iset) => iset-max-end)
         (else (iset-end iset))))
@@ -67,7 +62,7 @@
 
 (define (iset-squash-bits! iset)
   (let ((bits (iset-bits iset)))
-    (if (= bits (range->bits (iset-start iset) (iset-end iset)))
+    (if (and bits (= bits (range->bits (iset-start iset) (iset-end iset))))
         (iset-bits-set! iset #f))))
 
 (define (iset-adjoin1! iset n)
diff --git a/lib/chibi/iset/constructors.sld b/lib/chibi/iset/constructors.sld
index 605b7181..87baaf18 100644
--- a/lib/chibi/iset/constructors.sld
+++ b/lib/chibi/iset/constructors.sld
@@ -6,4 +6,6 @@
    iset iset-copy list->iset list->iset! iset-map
    iset-adjoin iset-adjoin! iset-delete iset-delete!
    iset-union iset-union! iset-intersection iset-intersection!
-   iset-difference iset-difference!))
+   iset-difference iset-difference!
+   ;; low-level
+   iset-copy-node iset-squash-bits! iset-insert-left! iset-insert-right!))
diff --git a/lib/chibi/iset/iterators.scm b/lib/chibi/iset/iterators.scm
index 3dfec65d..08889133 100644
--- a/lib/chibi/iset/iterators.scm
+++ b/lib/chibi/iset/iterators.scm
@@ -17,25 +17,27 @@
 
 ;; Create a new iset cursor pointing to the first element of iset,
 ;; with an optional stack argument.
-(define (iset-cursor iset . o)
+(define (%iset-cursor iset . o)
   (iset-cursor-advance
    (make-iset-cursor iset
                      (or (iset-bits iset) (iset-start iset))
                      (if (pair? o) (car o) '()))))
 
+(define (iset-cursor iset . o)
+  (let ((stack (if (pair? o) (car o) '())))
+    (if (iset-left iset)
+        (iset-cursor (iset-left iset) (cons iset stack))
+        (%iset-cursor iset stack))))
+
 ;; Continue to the next node in the search stack.
 (define (iset-cursor-pop cur)
   (let ((node (iset-cursor-node cur))
         (stack (iset-cursor-stack cur)))
     (cond
-     ((iset-left node)
-      (iset-cursor
-       (iset-left node)
-       (if (iset-right node) (cons (iset-right node) stack) stack)))
      ((iset-right node)
       (iset-cursor (iset-right node) stack))
      ((pair? stack)
-      (iset-cursor (car stack) (cdr stack)))
+      (%iset-cursor (car stack) (cdr stack)))
      (else
       cur))))
 
@@ -44,9 +46,10 @@
 (define (iset-cursor-advance cur)
   (let ((node (iset-cursor-node cur))
         (pos (iset-cursor-pos cur)))
-    (if (if (iset-bits node) (zero? pos) (> pos (iset-end node)))
-        (iset-cursor-pop cur)
-        cur)))
+    (cond
+     ((if (iset-bits node) (zero? pos) (> pos (iset-end node)))
+      (iset-cursor-pop cur))
+     (else cur))))
 
 (define (iset-cursor-next iset cur)
   (iset-cursor-advance
@@ -76,7 +79,6 @@
     (and (if (iset-bits node)
              (zero? (iset-cursor-pos cur))
              (> (iset-cursor-pos cur) (iset-end node)))
-         (not (iset-left node))
          (not (iset-right node))
          (null? (iset-cursor-stack cur)))))
 
@@ -90,7 +92,9 @@
           ((end-of-iset? cur2) #f)
           ((= (iset-ref is1 cur1) (iset-ref is2 cur2))
            (lp (iset-cursor-next is1 cur1) (iset-cursor-next is2 cur2)))
-          (else #f))))
+          (else
+           (write `(not (= ,(iset-ref is1 cur1) ,(iset-ref is2 cur2)))) (newline)
+           #f))))
 
 (define (iset2<= is1 is2)
   (let lp ((cur1 (iset-cursor is1))
diff --git a/lib/chibi/iset/iterators.sld b/lib/chibi/iset/iterators.sld
index cd044525..49b18e59 100644
--- a/lib/chibi/iset/iterators.sld
+++ b/lib/chibi/iset/iterators.sld
@@ -4,6 +4,6 @@
   (include "iterators.scm")
   (export
    iset-empty? iset-fold iset-fold-node iset-for-each iset-for-each-node
-   iset->list iset-size
+   iset->list iset-size iset= iset<= iset>=
    ;; low-level cursors
    iset-cursor iset-cursor? iset-cursor-next iset-ref end-of-iset?))