diff --git a/filter/decl.m4 b/filter/decl.m4
index 5242c04c..75e65212 100644
--- a/filter/decl.m4
+++ b/filter/decl.m4
@@ -494,6 +494,15 @@ f_const_promotion(struct f_inst *arg, enum f_type want)
     };
     return 1;
   }
+  else if ((c->type == T_SET) && (want == T_PREFIX_SET)) {
+    if (c->val.t)
+      return 0;
+    *c = (struct f_val) {
+      .type = T_PREFIX_SET,
+      .val.ti = f_new_trie(cfg_mem, 0),
+    };
+    return 1;
+  }
 
   return 0;
 }
diff --git a/filter/f-inst.c b/filter/f-inst.c
index b1d14b9d..999b7fc7 100644
--- a/filter/f-inst.c
+++ b/filter/f-inst.c
@@ -983,7 +983,7 @@
     RESULT(T_INT, i, v1.val.lc.ldp2);
   }
 
-  INST(FI_MIN, 1, 1) {	/* Get minimum element from set */
+  INST(FI_MIN, 1, 1) {	/* Get minimum element from list */
     ARG_ANY(1);
     RESULT_TYPE(f_type_element_type(v1.type));
     switch(v1.type)
@@ -1017,7 +1017,7 @@
     }
   }
 
-  INST(FI_MAX, 1, 1) {	/* Get maximum element from set */
+  INST(FI_MAX, 1, 1) {	/* Get maximum element from list */
     ARG_ANY(1);
     RESULT_TYPE(f_type_element_type(v1.type));
     switch(v1.type)
@@ -1215,15 +1215,18 @@
     {
       const struct f_tree *set = NULL;
       u32 key = 0;
+      int use_set = 0;
 
       if (v2.type == T_INT)
 	key = v2.val.i;
-      else if ((v2.type == T_SET) && path_set_type(v2.val.t))
+      else if ((v2.type == T_SET) && path_set_type(v2.val.t)) {
+	use_set = 1;
 	set = v2.val.t;
+      }
       else
 	runtime("Can't delete non-integer (set)");
 
-      RESULT_(T_PATH, ad, [[ as_path_filter(fpool, v1.val.ad, set, key, 0) ]]);
+      RESULT_(T_PATH, ad, [[ as_path_filter(fpool, v1.val.ad, set, key, use_set, 0) ]]);
     }
 
     else if (v1.type == T_CLIST)
@@ -1275,12 +1278,20 @@
 
     if (v1.type == T_PATH)
     {
+      const struct f_tree *set = NULL;
       u32 key = 0;
+      int use_set = 0;
 
-      if ((v2.type == T_SET) && path_set_type(v2.val.t))
-	RESULT_(T_PATH, ad, [[ as_path_filter(fpool, v1.val.ad, v2.val.t, key, 1) ]]);
+      if (v2.type == T_INT)
+	key = v2.val.i;
+      else if ((v2.type == T_SET) && path_set_type(v2.val.t)) {
+        use_set = 1;
+        set = v2.val.t;
+      }
       else
-	runtime("Can't filter integer");
+	runtime("Can't filter non-integer (set)");
+
+      RESULT_(T_PATH, ad, [[ as_path_filter(fpool, v1.val.ad, set, key, use_set, 1) ]]);
     }
 
     else if (v1.type == T_CLIST)
diff --git a/filter/test.conf b/filter/test.conf
index c0fe4e70..65c680cd 100644
--- a/filter/test.conf
+++ b/filter/test.conf
@@ -131,6 +131,13 @@ define is3 = [5, 17, 2, 11, 8, 15, 3, 19];
 function t_int_set()
 int set is;
 {
+	bt_assert([] = empty_set);
+	is = [];
+	is = empty_set;
+	bt_assert(is = empty_set);
+	bt_assert(is = []);
+	bt_assert(0 !~ is);
+
 	bt_assert(1 ~ [1,2,3]);
 	bt_assert(5 ~ [1..20]);
 	bt_assert(2 ~ [ 1, 2, 3 ]);
@@ -139,6 +146,7 @@ int set is;
 	bt_assert(999 !~ [ 666, 333 ]);
 	bt_assert(1 !~ []);
 	bt_assert(1 !~ empty_set);
+	bt_assert(1 !~ is);
 
 	is = [ 2, 3, 4, 7..11 ];
 	bt_assert(10 ~ is);
@@ -171,7 +179,6 @@ int set is;
 
 	bt_assert([1,2] != [1,3]);
 	bt_assert([1,4..10,20] = [1,4..10,20]);
-	bt_assert([] = empty_set);
 
 	bt_assert(format([ 1, 2, 1, 1, 1, 3, 4, 1, 1, 1, 5 ]) = "[1, 1, 1, 1, 1, 1, 1, 2, 3, 4, 5]");
 	bt_assert(format([]) = "[]");
@@ -241,6 +248,9 @@ function t_pair_set()
 pair pp;
 pair set ps;
 {
+	ps = [];
+	ps = empty_set;
+
 	pp = (1, 2);
 	ps = [(1,(one+one)), (3,4)..(4,8), (5,*), (6,3..6)];
 	bt_assert(format(ps) = "[(1,2), (3,4)..(4,8), (5,0)..(5,65535), (6,3)..(6,6)]");
@@ -381,6 +391,9 @@ define ip1222 = 1.2.2.2;
 function t_ip_set()
 ip set ips;
 {
+	ips = [];
+	ips = empty_set;
+
 	ips = [ 1.1.1.0 .. 1.1.1.255, ip1222];
 	bt_assert(format(ips) = "[1.1.1.0..1.1.1.255, 1.2.2.2]");
 	bt_assert(1.1.1.0 ~ ips);
@@ -493,6 +506,15 @@ function test_pxset(prefix set pxs)
 function t_prefix_set()
 prefix set pxs;
 {
+	pxs = [];
+	pxs = empty_set;
+	bt_assert(format(pxs) = "[]");
+	#bt_assert(pxs = []);
+	#bt_assert(pxs = empty_set);
+	bt_assert(1.2.0.0/16 !~ []);
+	bt_assert(1.2.0.0/16 !~ empty_set);
+	bt_assert(1.2.0.0/16 !~ pxs);
+
 	pxs = [ 1.2.0.0/16, 1.4.0.0/16+, 44.66.88.64/30{24,28}, 12.34.56.0/24{8,16} ];
 	bt_assert(format(pxs) = "[1.2.0.0/16{0.1.0.0}, 1.4.0.0/16{0.1.255.255}, 12.34.0.0/16{1.255.0.0}, 44.66.88.64/28{0.0.1.240}]");
 
@@ -577,6 +599,15 @@ bt_test_suite(t_prefix6, "Testing prefix IPv6");
 function t_prefix6_set()
 prefix set pxs;
 {
+	pxs = [];
+	pxs = empty_set;
+	bt_assert(format(pxs) = "[]");
+	#bt_assert(pxs = []);
+	#bt_assert(pxs = empty_set);
+	bt_assert(12::34/128 !~ []);
+	bt_assert(12::34/128 !~ empty_set);
+	bt_assert(12::34/128 !~ pxs);
+
 	bt_assert(1180::/16 ~ [ 1100::/8{15, 17} ]);
 	bt_assert(12::34 = 12::34);
 	bt_assert(12::34 ~ [ 12::33..12::35 ]);
@@ -586,8 +617,6 @@ prefix set pxs;
 	bt_assert(12::34 !~ [ 12::33, 12::35 ]);
 	bt_assert(1000::/9 !~ [ 1000::/8- ]);
 	bt_assert(1000::/17 !~ [ 1000::/8{15, 16} ]);
-	bt_assert(12::34 !~ []);
-	bt_assert(12::34 !~ empty_set);
 
 	pxs = [ 1102::/16, 1104::/16+];
 	bt_assert(1102::/16  ~ pxs);
@@ -711,8 +740,6 @@ int set set12;
 	bt_assert(p2 ~ [= * [3] * =]);
 	bt_assert(p2 !~ [= * [] * =]);
 	bt_assert(p2 !~ [= * empty_set * =]);
-	#bt_assert(delete(prepend(prepend(+empty+, 0), 1), []) = prepend(+empty+, 1));
-	#bt_assert(filter(prepend(prepend(+empty+, 0), 1), []) = prepend(+empty+, 0));
 
 	bt_assert(p2.len = 5);
 	bt_assert(p2.first = 5);
@@ -723,6 +750,8 @@ int set set12;
 	bt_assert(filter(p2, [1..3]) = prepend(prepend(prepend(+empty+, 1), 2), 3));
 	bt_assert(delete(p2, []) = p2);
 	bt_assert(filter(p2, []) = +empty+);
+	bt_assert(delete(prepend(prepend(+empty+, 0), 1), []) = prepend(prepend(+empty+, 0), 1));
+	bt_assert(filter(prepend(prepend(+empty+, 0), 1), []) = +empty+);
 
 	p2 = prepend( + empty +, 5 );
 	p2 = prepend( p2, 4 );
@@ -1189,6 +1218,12 @@ bt_test_suite(t_rd, "Testing route distinguishers");
 function t_rd_set()
 rd set rds;
 {
+	rds = [];
+	rds = empty_set;
+	bt_assert(rds = []);
+	bt_assert(rds = empty_set);
+	bt_assert(10:20 !~ rds);
+
 	rds = [10:20, 100000:100..100000:200];
 	bt_assert(format(rds)  = "[10:20, 100000:100..100000:200]");
 
diff --git a/nest/a-path.c b/nest/a-path.c
index 2e34a3d1..ed4457b0 100644
--- a/nest/a-path.c
+++ b/nest/a-path.c
@@ -602,7 +602,7 @@ as_path_match_set(const struct adata *path, const struct f_tree *set)
 }
 
 const struct adata *
-as_path_filter(struct linpool *pool, const struct adata *path, const struct f_tree *set, u32 key, int pos)
+as_path_filter(struct linpool *pool, const struct adata *path, const struct f_tree *set, u32 key, int use_set, int pos)
 {
   if (!path)
     return NULL;
@@ -629,7 +629,7 @@ as_path_filter(struct linpool *pool, const struct adata *path, const struct f_tr
 	  u32 as = get_as(p);
 	  int match;
 
-	  if (set)
+	  if (use_set)
 	    {
 	      struct f_val v = {T_INT, .val.i = as};
 	      match = !!find_tree(set, &v);
diff --git a/nest/a-path_test.c b/nest/a-path_test.c
index 9ed0a786..e02c6fd0 100644
--- a/nest/a-path_test.c
+++ b/nest/a-path_test.c
@@ -136,8 +136,8 @@ t_path_include(void)
     int counts_of_contains = count_asn_in_array(as_nums, as_nums[i]);
     bt_assert_msg(as_path_contains(as_path, as_nums[i], counts_of_contains), "AS Path should contains %d-times number %d", counts_of_contains, as_nums[i]);
 
-    bt_assert(as_path_filter(lp, as_path, NULL, as_nums[i], 0) != NULL);
-    bt_assert(as_path_filter(lp, as_path, NULL, as_nums[i], 1) != NULL);
+    bt_assert(as_path_filter(lp, as_path, NULL, as_nums[i], 0, 0) != NULL);
+    bt_assert(as_path_filter(lp, as_path, NULL, as_nums[i], 0, 1) != NULL);
   }
 
   for (i = 0; i < 10000; i++)
diff --git a/nest/attrs.h b/nest/attrs.h
index ef2b95e6..c92a8826 100644
--- a/nest/attrs.h
+++ b/nest/attrs.h
@@ -49,7 +49,7 @@ int as_path_get_last(const struct adata *path, u32 *last_as);
 u32 as_path_get_last_nonaggregated(const struct adata *path);
 int as_path_contains(const struct adata *path, u32 as, int min);
 int as_path_match_set(const struct adata *path, const struct f_tree *set);
-const struct adata *as_path_filter(struct linpool *pool, const struct adata *path, const struct f_tree *set, u32 key, int pos);
+const struct adata *as_path_filter(struct linpool *pool, const struct adata *path, const struct f_tree *set, u32 key, int use_set, int pos);
 
 static inline struct adata *as_path_prepend(struct linpool *pool, const struct adata *path, u32 as)
 { return as_path_prepend2(pool, path, AS_PATH_SEQUENCE, as); }