use macro for /usr/local/plan9
diff --git a/man/man3/lock.3 b/man/man3/lock.3
index 9034229..4308e36 100644
--- a/man/man3/lock.3
+++ b/man/man3/lock.3
@@ -193,9 +193,9 @@
 .B Ref
 and returns zero if the resulting value is zero, non-zero otherwise.
 .SH SOURCE
-.B /usr/local/plan9/src/lib9/qlock.c
+.B \*9/src/lib9/qlock.c
 .br
-.B /usr/local/plan9/src/libthread
+.B \*9/src/libthread
 .SH BUGS
 .B Locks
 are not always spin locks.