use macro for /usr/local/plan9
diff --git a/man/man4/plumber.4 b/man/man4/plumber.4
index 681bd5e..95259a0 100644
--- a/man/man4/plumber.4
+++ b/man/man4/plumber.4
@@ -101,7 +101,7 @@
 .B /usr/$user/lib/plumbing
 default rules file
 .TP
-.B /usr/local/plan9/plumb
+.B \*9/plumb
 directory to search for files in
 .B include
 statements
@@ -110,7 +110,7 @@
 mount name for
 .IR plumber (4).
 .SH SOURCE
-.B /usr/local/plan9/src/cmd/plumb
+.B \*9/src/cmd/plumb
 .SH "SEE ALSO"
 .IR plumb (1),
 .IR plumb (3),