Update reference to Robert C. Martin's "Acyclic Visitor" paper.

The source at objectmentor.com has been unavailble for a long while.

diff --git a/ginac/basic.h b/ginac/basic.h
index 3ae3282c3e7ce32c8ba1b85adb37615ed845db03..1af6f85844ca68683f2eb3a0111d6fcf02578a20 100644 (file)
--- a/ginac/basic.h
+++ b/ginac/basic.h
@@ -92,7 +92,8 @@ struct map_function {
 
 /** Degenerate base class for visitors. basic and derivative classes
  *  support Robert C. Martin's Acyclic Visitor pattern (cf.
 
 /** Degenerate base class for visitors. basic and derivative classes
  *  support Robert C. Martin's Acyclic Visitor pattern (cf.

- *  http://objectmentor.com/publications/acv.pdf). */
+ *  http://condor.depaul.edu/dmumaugh/OOT/Design-Principles/acv.pdf
+ *  or chapter 10 of Andrei Alexandrescu's "Modern C++ Design"). */

 class visitor {
 protected:
        virtual ~visitor() {}
 class visitor {
 protected:
        virtual ~visitor() {}