diff --git a/mixin/builtins.py b/mixin/builtins.py
index b408f4c1..8a1ead90 100644
--- a/mixin/builtins.py
+++ b/mixin/builtins.py
@@ -109,6 +109,18 @@ class set():
         return self
 
 
+class frozenset():
+    def __init__(self, iterable=[]):
+        self.iterable = iterable
+
+    def __iter__(self):
+        for i in self.iterable:
+            yield i
+
+    def copy(self):
+        return self
+
+
 #--------------------------------------------------------
 # basic types
 #--------------------------------------------------------
diff --git a/test/completion/arrays.py b/test/completion/arrays.py
index 705b1507..8900da9a 100644
--- a/test/completion/arrays.py
+++ b/test/completion/arrays.py
@@ -187,8 +187,23 @@ GetItem("")[1]
 # conversions
 # -----------------
 
+a = [1, ""]
 #? int() str()
-list([1,""])[1]
+list(a)[1]
 
 #? int() str()
-list(set([1,""]))[1]
+list(a)[0]
+
+#? int() str()
+list(set(a))[1]
+#? int() str()
+list(list(set(a)))[1]
+
+# does not yet work, because the recursion catching is not good enough (catches # to much)
+##? int() str()
+list(set(list(set(a))))[1]
+##? int() str()
+list(set(set(a)))[1]
+
+#? int() str()
+list(frozenset(a))[1]