diff --git a/minimart/gestalt.rkt b/minimart/gestalt.rkt
index be7fa9e..c9b17ca 100644
--- a/minimart/gestalt.rkt
+++ b/minimart/gestalt.rkt
@@ -168,16 +168,11 @@
 
 ;; View on g1 from g2's perspective.
 (define (gestalt-filter g1 g2)
-  (parameterize ((matcher-union-successes (lambda (v1 v2)
-					    (match* (v1 v2)
-					      [(#t v) v]
-					      [(v #t) v]
-					      [(v1 v2) (set-union v1 v2)]))))
-    (gestalt (map-zip shorter-imbalance-handler
-		      filter-one-metalevel
-		      cons-metalevel
-		      (gestalt-metalevels g1)
-		      (gestalt-metalevels g2)))))
+  (gestalt (map-zip shorter-imbalance-handler
+		    filter-one-metalevel
+		    cons-metalevel
+		    (gestalt-metalevels g1)
+		    (gestalt-metalevels g2))))
 
 ;; Much like gestalt-filter, takes a view on gestalt g1 from g2's
 ;; perspective. However, instead of returning the filtered g1, returns
diff --git a/minimart/route.rkt b/minimart/route.rkt
index 030a6ca..26e97f2 100644
--- a/minimart/route.rkt
+++ b/minimart/route.rkt
@@ -35,7 +35,11 @@
 	 matcher-project-success)
 
 ;; TODO: perhaps avoid the parameters on the fast-path, if they are causing measurable slowdown.
-(define matcher-union-successes (make-parameter set-union))
+(define matcher-union-successes (make-parameter (lambda (v1 v2)
+						  (match* (v1 v2)
+						    [(#t v) v]
+						    [(v #t) v]
+						    [(v1 v2) (set-union v1 v2)]))))
 (define matcher-intersect-successes (make-parameter set-union))
 (define matcher-erase-path-successes (make-parameter (lambda (s1 s2)
 						       (define r (set-subtract s1 s2))
@@ -1106,6 +1110,22 @@
 			 (list (pattern->matcher #t (vector 1 4))
 			       (pattern->matcher #t (vector 3 4)))))
 
+    (check-equal? (matcher-key-set
+		   (matcher-project (foldr matcher-union (matcher-empty)
+					   (list (pattern->matcher SA (cons 1 2))
+						 (pattern->matcher SC (cons ? 3))
+						 (pattern->matcher SB (cons 3 4))))
+				    (compile-projection (cons (?!) (?!)))))
+		  #f)
+
+    (check-equal? (matcher-key-set
+		   (matcher-project (foldr matcher-union (matcher-empty)
+					   (list (pattern->matcher SA (cons ? 2))
+						 (pattern->matcher SC (cons 1 3))
+						 (pattern->matcher SB (cons 3 4))))
+				    (compile-projection (cons ? (?!)))))
+		  (set '#(2) '#(3) '#(4)))
+
     (check-equal? (matcher-key-set
 		   (matcher-project (matcher-union (pattern->matcher SA (cons 1 2))
 						   (pattern->matcher SB (cons 3 4)))
@@ -1123,4 +1143,4 @@
   (check-equal? (projection->pattern (list 'a (?! 'b))) (list 'a 'b))
   (check-equal? (projection->pattern (list 'a (?! (vector 'b)))) (list 'a (vector 'b)))
   (check-equal? (projection->pattern (list 'a (?! (vector ? ?)))) (list 'a (vector ? ?)))
-  )
\ No newline at end of file
+  )