diff --git a/lemon/howard.h b/lemon/howard.h
--- a/lemon/howard.h
+++ b/lemon/howard.h
@@ -97,7 +97,8 @@
   /// mean cycle.
   ///
   /// This class implements Howard's policy iteration algorithm for finding
-  /// a directed cycle of minimum mean length (cost) in a digraph.
+  /// a directed cycle of minimum mean length (cost) in a digraph
+  /// \ref amo93networkflows, \ref dasdan98minmeancycle.
   /// This class provides the most efficient algorithm for the
   /// minimum mean cycle problem, though the best known theoretical
   /// bound on its running time is exponential.