use macro for /usr/local/plan9
diff --git a/man/man3/open.3 b/man/man3/open.3
index b964cc9..51ff2cd 100644
--- a/man/man3/open.3
+++ b/man/man3/open.3
@@ -138,7 +138,7 @@
 .I close
 allows the file descriptor to be reused.
 .SH SOURCE
-.B /usr/local/plan9/src/lib9
+.B \*9/src/lib9
 .SH SEE ALSO
 .IR intro (3),
 .IR stat (3)