diff --git a/syndicate/skeleton.rkt b/syndicate/skeleton.rkt
index c130c4f..14a33c2 100644
--- a/syndicate/skeleton.rkt
+++ b/syndicate/skeleton.rkt
@@ -117,7 +117,7 @@
 (define (skcont-add! c i)
   (match-define (skeleton-interest _desc cs cv vs h _cleanup) i)
   (define (make-matched-constant)
-    (skeleton-matched-constant (for/mutable-set [(a (skeleton-continuation-cache c))
+    (skeleton-matched-constant (for/mutable-set [(a (in-set (skeleton-continuation-cache c)))
                                                  #:when (equal? (apply-projection a cs) cv)]
                                  a)
                                (make-hash)))
@@ -125,7 +125,7 @@
   (define sc (hash-ref! cvt cv make-matched-constant))
   (define (make-accumulator)
     (define cache (make-bag))
-    (for [(a (skeleton-matched-constant-cache sc))]
+    (for [(a (in-set (skeleton-matched-constant-cache sc)))]
       (define vars (apply-projection a vs))
       (bag-change! cache vars 1))
     (skeleton-accumulator cache (mutable-seteq)))
@@ -181,7 +181,7 @@
        (define (make-skeleton-node-with-cache)
          (define unfiltered (skeleton-continuation-cache (skeleton-node-continuation sk)))
          (make-empty-skeleton/cache
-          (for/mutable-set [(a unfiltered) #:when (subterm-matches-class? a path class)] a)))
+          (for/mutable-set [(a (in-set unfiltered)) #:when (subterm-matches-class? a path class)] a)))
        (define next (hash-ref! table class make-skeleton-node-with-cache))
        (walk-edge! (update-path path pop-count 0) next 0 0 pieces)]
       [_
@@ -218,7 +218,7 @@
           (define variables (apply-projection term0 variable-proj))
           (modify-skacc! acc variables term0))))
 
-    (for [(edge edges)]
+    (for [(edge (in-list edges))]
       (match-define (cons (skeleton-selector pop-count index) table) edge)
       (define popped-stack (drop term-stack pop-count))
       (define pieces (car popped-stack))
@@ -243,7 +243,7 @@
 (define (add-term-to-skacc! skacc vars _term)
   (match (bag-change! (skeleton-accumulator-cache skacc) vars 1)
     ['absent->present
-     (for [(handler (skeleton-accumulator-handlers skacc))]
+     (for [(handler (in-set (skeleton-accumulator-handlers skacc)))]
        (apply handler '+ vars))]
     ;; 'present->absent and 'absent->absent absurd
     ['present->present
@@ -265,7 +265,7 @@
   (if (bag-member? cache vars)
       (match (bag-change! cache vars -1)
         ['present->absent
-         (for [(handler (skeleton-accumulator-handlers skacc))]
+         (for [(handler (in-set (skeleton-accumulator-handlers skacc)))]
            (apply handler '- vars))]
         ;; 'absent->absent and 'absent->present absurd
         ['present->present
@@ -285,16 +285,16 @@
                     void
                     void
                     (lambda (skacc vars _term)
-                      (for [(handler (skeleton-accumulator-handlers skacc))]
+                      (for [(handler (in-set (skeleton-accumulator-handlers skacc)))]
                         (apply handler '! vars)))))
 
 ;; TODO: avoid repeated descent into `term` by factoring out prefixes of paths in `proj`
 (define (apply-projection term proj)
-  (for/list [(path proj)]
+  (for/list [(path (in-list proj))]
     (apply-projection-path term path)))
 
 (define (apply-projection-path term path)
-  (for/fold [(term (list term))] [(index path)]
+  (for/fold [(term (list term))] [(index (in-list path))]
     (cond [(list? term) (list-ref term index)]
           [(non-object-struct? term) (vector-ref (struct->vector term) (+ index 1))]
           [else (error 'apply-projection "Term representation not supported: ~v" term)])))