diff -r 4a170261cc54 -r da87dbdf3daf lemon/concepts/graph.h
--- a/lemon/concepts/graph.h	Thu Feb 25 09:46:12 2021 +0100
+++ b/lemon/concepts/graph.h	Tue Jul 28 21:23:36 2020 +0200
@@ -108,6 +108,11 @@
         /// Copy constructor.
         ///
         Node(const Node&) { }
+        /// Assignment operator
+
+        /// Assignment operator.
+        ///
+        const Node &operator=(const Node&) { return *this; }
 
         /// %Invalid constructor \& conversion.
 
@@ -159,6 +164,12 @@
         /// Copy constructor.
         ///
         NodeIt(const NodeIt& n) : Node(n) { }
+        /// Assignment operator
+
+        /// Assignment operator.
+        ///
+        const NodeIt &operator=(const NodeIt&) { return *this; }
+
         /// %Invalid constructor \& conversion.
 
         /// Initializes the iterator to be invalid.
@@ -218,6 +229,12 @@
         /// Copy constructor.
         ///
         Edge(const Edge&) { }
+        /// Assignment operator
+
+        /// Assignment operator.
+        ///
+        const Edge &operator=(const Edge&) { return *this; }
+
         /// %Invalid constructor \& conversion.
 
         /// Initializes the object to be invalid.
@@ -266,6 +283,12 @@
         /// Copy constructor.
         ///
         EdgeIt(const EdgeIt& e) : Edge(e) { }
+        /// Assignment operator
+
+        /// Assignment operator.
+        ///
+        const EdgeIt &operator=(const EdgeIt&) { return *this; }
+
         /// %Invalid constructor \& conversion.
 
         /// Initializes the iterator to be invalid.
@@ -335,6 +358,12 @@
         /// Copy constructor.
         ///
         IncEdgeIt(const IncEdgeIt& e) : Edge(e) { }
+        /// Assignment operator
+
+        /// Assignment operator.
+        ///
+        const IncEdgeIt &operator=(const IncEdgeIt&) { return *this; }
+
         /// %Invalid constructor \& conversion.
 
         /// Initializes the iterator to be invalid.
@@ -396,6 +425,12 @@
         /// Copy constructor.
         ///
         Arc(const Arc&) { }
+        /// Assignment operator
+
+        /// Assignment operator.
+        ///
+        const Arc &operator=(const Arc&) { return *this; }
+
         /// %Invalid constructor \& conversion.
 
         /// Initializes the object to be invalid.
@@ -450,6 +485,12 @@
         /// Copy constructor.
         ///
         ArcIt(const ArcIt& e) : Arc(e) { }
+        /// Assignment operator
+
+        /// Assignment operator.
+        ///
+        const ArcIt &operator=(const ArcIt&) { return *this; }
+
         /// %Invalid constructor \& conversion.
 
         /// Initializes the iterator to be invalid.
@@ -518,6 +559,12 @@
         /// Copy constructor.
         ///
         OutArcIt(const OutArcIt& e) : Arc(e) { }
+        /// Assignment operator
+
+        /// Assignment operator.
+        ///
+        const OutArcIt &operator=(const OutArcIt&) { return *this; }
+
         /// %Invalid constructor \& conversion.
 
         /// Initializes the iterator to be invalid.
@@ -587,6 +634,12 @@
         /// Copy constructor.
         ///
         InArcIt(const InArcIt& e) : Arc(e) { }
+        /// Assignment operator
+
+        /// Assignment operator.
+        ///
+        const InArcIt &operator=(const InArcIt&) { return *this; }
+
         /// %Invalid constructor \& conversion.
 
         /// Initializes the iterator to be invalid.
@@ -651,6 +704,10 @@
         NodeMap(const NodeMap& nm) :
           ReferenceMap<Node, T, T&, const T&>(nm) { }
         ///Assignment operator
+        NodeMap& operator=(const NodeMap&) {
+          return *this;
+        }
+        ///Template Assignment operator
         template <typename CMap>
         NodeMap& operator=(const CMap&) {
           checkConcept<ReadMap<Node, T>, CMap>();
@@ -677,6 +734,10 @@
         ArcMap(const ArcMap& em) :
           ReferenceMap<Arc, T, T&, const T&>(em) { }
         ///Assignment operator
+        ArcMap& operator=(const ArcMap&) {
+          return *this;
+        }
+        ///Template Assignment operator
         template <typename CMap>
         ArcMap& operator=(const CMap&) {
           checkConcept<ReadMap<Arc, T>, CMap>();
@@ -703,6 +764,10 @@
         EdgeMap(const EdgeMap& em) :
           ReferenceMap<Edge, T, T&, const T&>(em) {}
         ///Assignment operator
+        EdgeMap& operator=(const EdgeMap&) {
+          return *this;
+        }
+        ///Template Assignment operator
         template <typename CMap>
         EdgeMap& operator=(const CMap&) {
           checkConcept<ReadMap<Edge, T>, CMap>();