diff --git a/relation.rkt b/relation.rkt
index a2417fe..eeb3018 100644
--- a/relation.rkt
+++ b/relation.rkt
@@ -11,6 +11,7 @@
 
 	 relation->hash
 	 in-relation-domain
+	 in-relation/grouped
 
 	 relation-empty?
 	 relation-count
@@ -76,6 +77,9 @@
 (define (in-relation-domain r)
   (in-hash-keys (relation-table r)))
 
+(define (in-relation/grouped r)
+  (in-hash (relation-table r)))
+
 (define (relation-empty? r)
   (zero? (hash-count (relation-table r))))