diff -ru boost_1_34_0/libs/graph/src/graphviz_graph_lex.cpp boost_1_34_0_ibm/libs/graph/src/graphviz_graph_lex.cpp
--- boost_1_34_0/libs/graph/src/graphviz_graph_lex.cpp	2006-11-03 15:17:56.000000000 -0400
+++ boost_1_34_0_ibm/libs/graph/src/graphviz_graph_lex.cpp	2007-05-17 18:59:00.000000000 -0400
@@ -1411,9 +1411,12 @@
 
 #ifndef YY_ALWAYS_INTERACTIVE
 #ifndef YY_NEVER_INTERACTIVE
+/* Avoid conflicts if isatty() has a different prototype in <unistd.h>. */
+#if !defined(__IBMCPP__)
 extern int isatty YY_PROTO(( int ));
 #endif
 #endif
+#endif
 
 #ifdef YY_USE_PROTOS
 void yy_init_buffer( YY_BUFFER_STATE b, FILE *file )