diff -r 0759d974de81 -r 4add05447ca0 lemon/bits/graph_adaptor_extender.h
--- a/lemon/bits/graph_adaptor_extender.h	Sun Jan 05 22:24:56 2014 +0100
+++ b/lemon/bits/graph_adaptor_extender.h	Tue Apr 14 08:39:40 2015 +0200
@@ -85,7 +85,7 @@
 
     };
 
-    LemonRangeWrapper1<NodeIt, Adaptor> nodes() {
+    LemonRangeWrapper1<NodeIt, Adaptor> nodes() const {
       return LemonRangeWrapper1<NodeIt, Adaptor>(*this);
     }
 
@@ -111,7 +111,7 @@
 
     };
 
-    LemonRangeWrapper1<ArcIt, Adaptor> arcs() {
+    LemonRangeWrapper1<ArcIt, Adaptor> arcs() const {
       return LemonRangeWrapper1<ArcIt, Adaptor>(*this);
     }
 
@@ -269,7 +269,7 @@
 
     };
 
-    LemonRangeWrapper1<NodeIt, Adaptor> nodes() {
+    LemonRangeWrapper1<NodeIt, Adaptor> nodes() const {
       return LemonRangeWrapper1<NodeIt, Adaptor>(*this);
     }
 
@@ -296,7 +296,7 @@
 
     };
 
-    LemonRangeWrapper1<ArcIt, Adaptor> arcs() {
+    LemonRangeWrapper1<ArcIt, Adaptor> arcs() const {
       return LemonRangeWrapper1<ArcIt, Adaptor>(*this);
     }
 
@@ -378,7 +378,7 @@
 
     };
 
-    LemonRangeWrapper1<EdgeIt, Adaptor> edges() {
+    LemonRangeWrapper1<EdgeIt, Adaptor> edges() const {
       return LemonRangeWrapper1<EdgeIt, Adaptor>(*this);
     }