use macro for /usr/local/plan9
diff --git a/man/man3/rc4.3 b/man/man3/rc4.3
index ba848d9..026c835 100644
--- a/man/man3/rc4.3
+++ b/man/man3/rc4.3
@@ -41,7 +41,7 @@
 .I RC4state
 structure keeps track of the algorithm.
 .SH SOURCE
-.B /usr/local/plan9/src/libsec
+.B \*9/src/libsec
 .SH SEE ALSO
 .IR mp (3),
 .IR aes (3),