$NetBSD: patch-aa,v 1.1 2010/02/10 15:31:25 joerg Exp $

--- pyPdf/pdf.py.orig	2010-02-10 16:10:11.000000000 +0100
+++ pyPdf/pdf.py
@@ -49,7 +49,6 @@ import utils
 import warnings
 from generic import *
 from utils import readNonWhitespace, readUntilWhitespace, ConvertFunctionsToVirtualList
-from sets import ImmutableSet
 
 ##
 # This class supports writing PDF files out, given pages produced by another
@@ -986,8 +985,8 @@ class PageObject(DictionaryObject):
 
         # Combine /ProcSet sets.
         newResources[NameObject("/ProcSet")] = ArrayObject(
-            ImmutableSet(originalResources.get("/ProcSet", ArrayObject()).getObject()).union(
-                ImmutableSet(page2Resources.get("/ProcSet", ArrayObject()).getObject())
+            frozenset(originalResources.get("/ProcSet", ArrayObject()).getObject()).union(
+                frozenset(page2Resources.get("/ProcSet", ArrayObject()).getObject())
             )
         )