diff --git a/prospect-monolithic/mux.rkt b/prospect-monolithic/mux.rkt
index 5021888..727db45 100644
--- a/prospect-monolithic/mux.rkt
+++ b/prospect-monolithic/mux.rkt
@@ -95,7 +95,7 @@
 (define (compute-affected-pids routing-table cover)
   (trie-match-trie cover
 		   (trie-step routing-table struct:observe)
-		   #:seed (datum-tset)
+		   #:seed datum-tset-empty
 		   #:combiner (lambda (v1 v2 acc) (tset-union v2 acc))
 		   #:left-short (lambda (v r acc)
 				  (tset-union acc (success-value (trie-step r EOS))))))
@@ -103,7 +103,7 @@
 (define (mux-route-message m body)
   (if (trie-lookup (mux-routing-table m) body #f) ;; some other stream has declared body
       '()
-      (tset->list (trie-lookup (mux-routing-table m) (observe body) (datum-tset)))))
+      (tset->list (trie-lookup (mux-routing-table m) (observe body) datum-tset-empty))))
 
 (define (mux-interests-of m label)
   (hash-ref (mux-interest-table m) label (trie-empty)))
diff --git a/prospect/mux.rkt b/prospect/mux.rkt
index 499417d..fe1ed65 100644
--- a/prospect/mux.rkt
+++ b/prospect/mux.rkt
@@ -112,7 +112,7 @@
   (define cover (trie-union (patch-added delta) (patch-removed delta)))
   (trie-match-trie cover
 		   (trie-step routing-table struct:observe)
-		   #:seed (datum-tset)
+		   #:seed datum-tset-empty
 		   #:combiner (lambda (v1 v2 acc) (tset-union v2 acc))
 		   #:left-short (lambda (v r acc)
 				  (tset-union acc (success-value (trie-step r EOS))))))
@@ -120,7 +120,7 @@
 (define (mux-route-message m body)
   (if (trie-lookup (mux-routing-table m) body #f) ;; some other stream has declared body
       '()
-      (tset->list (trie-lookup (mux-routing-table m) (observe body) (datum-tset)))))
+      (tset->list (trie-lookup (mux-routing-table m) (observe body) datum-tset-empty))))
 
 (define (mux-interests-of m label)
   (hash-ref (mux-interest-table m) label (trie-empty)))
diff --git a/prospect/tset.rkt b/prospect/tset.rkt
index 735f0e1..a6e7361 100644
--- a/prospect/tset.rkt
+++ b/prospect/tset.rkt
@@ -4,6 +4,7 @@
 
 (provide tset?
          datum-tset
+         datum-tset-empty
          make-tset
          tset-count
          tset-empty
@@ -72,6 +73,8 @@
 (define (tset-member? t k)
   (treap-has-key? t k))
 
+(define datum-tset-empty (datum-tset))
+
 (module+ test
   (require rackunit)
   (require data/order)