use macro for /usr/local/plan9
diff --git a/man/man3/mach-map.3 b/man/man3/mach-map.3
index 2fc8cc7..45f48e7 100644
--- a/man/man3/mach-map.3
+++ b/man/man3/mach-map.3
@@ -395,7 +395,7 @@
 .I rput
 function families as necessary.
 .SH SOURCE
-.B /usr/local/plan9/src/libmach
+.B \*9/src/libmach
 .SH "SEE ALSO"
 .IR mach (3),
 .IR mach-file (3)