diff --git a/csp/constraint.rkt b/csp/constraint.rkt
index c0d54a09..e1c763f6 100644
--- a/csp/constraint.rkt
+++ b/csp/constraint.rkt
@@ -53,7 +53,7 @@
            (unless (is-true? variables domains assignments)
              (send unassigned-variable-domain hide-value value)))
          (hash-remove! assignments unassigned-variable)
-         (not (null? unassigned-variable-domain))] ; if domain had no remaining values, the constraint will be impossible to meet, so return #f
+         (not (empty? unassigned-variable-domain))] ; if domain had no remaining values, the constraint will be impossible to meet, so return #f
         [else #t]))
     ))
 
@@ -96,7 +96,7 @@
                         [assigned-value (in-list assigned-values)]
                         #:when (member assigned-value (unassigned-var-domain)))
                 (send unassigned-var-domain hide-value assigned-value)
-                (null? unassigned-var-domain))) #f] ; if domain had no remaining values, the constraint will be impossible to meet, so return #f
+                (empty? unassigned-var-domain))) #f] ; if domain had no remaining values, the constraint will be impossible to meet, so return #f
         [else #t]))))
 
 (define all-different-constraint%? (is-a?/c all-different-constraint%))
diff --git a/csp/helper.rkt b/csp/helper.rkt
index fbe1ecdd..c607c9ea 100644
--- a/csp/helper.rkt
+++ b/csp/helper.rkt
@@ -7,7 +7,7 @@
   (for ([i (in-naturals)])
     expr ...))
 
-(define-syntax-rule (forever/or expr ...)
+(define-syntax-rule (forever/until expr ...)
   (for/or ([i (in-naturals)])
     expr ...))
 
diff --git a/csp/solver.rkt b/csp/solver.rkt
index 301adb31..491f9104 100644
--- a/csp/solver.rkt
+++ b/csp/solver.rkt
@@ -15,7 +15,7 @@
 
 (struct vvp (variable values pushdomains))
 (define-syntax-rule (pop-vvp-values! vvps)
-  (if (null? vvps)
+  (if (empty? vvps)
       (error 'pop-vvp-values! (format "~a is null" vvps))
       (let ([vvp (car vvps)])
         (set! vvps (cdr vvps))
@@ -29,11 +29,11 @@
     (field [_forwardcheck forwardcheck]) 
     
     (define/override (get-solution-iter domains constraints vconstraints)
-      (define sorted-variables 
-        (map third (sort (map (λ(var)
-                                (list (- (length (hash-ref vconstraints var))) ; first two elements used for sorting 
-                                      (length ((hash-ref domains var)))
-                                      var)) (hash-keys domains)) list-comparator)))
+      (define sorted-variables (sort (hash-keys domains) list-comparator
+                                      #:key (λ(var)
+                                              (list (- (length (hash-ref vconstraints var)))
+                                                    (length ((hash-ref domains var)))
+                                                    var))))
       ;; state-retention variables
       (define possible-solution (make-hash))
       (define variable-queue null)
@@ -64,17 +64,17 @@
         (forever
          (unless (get-next-unassigned-variable)
            (yield (hash-copy possible-solution)) ; if there are no unassigned variables, solution is complete.
-           (if (null? variable-queue) ; then, if queue is empty ...
+           (if (empty? variable-queue)
                (exit-k) ; all done, no other solutions possible.
-               (set!-previous-variable))) ; or queue is not empty, so return to previous variable
+               (set!-previous-variable))) ; otherwise return to previous variable
          
          (let value-checking-loop () ; we have a variable. Do we have any values left?
-           (when (null? values) ; no, so try going back to last variable and getting some values
-             (forever/or
-              (when (null? variable-queue) (exit-k)) ; no variables left, so solver is done
+           (when (empty? values) ; no, so try going back to last variable and getting some values
+             (forever/until
+              (when (empty? variable-queue) (exit-k)) ; no variables left, so solver is done
               (hash-remove! possible-solution variable)
               (set!-previous-variable)
-              (not (null? values))))        
+              (not (empty? values))))        
            
            ;; Got a value. Check it.
            (hash-set! possible-solution variable (car-pop! values))