use macro for /usr/local/plan9
diff --git a/man/man3/rsa.3 b/man/man3/rsa.3
index c0b0fe9..0c1396a 100644
--- a/man/man3/rsa.3
+++ b/man/man3/rsa.3
@@ -239,7 +239,7 @@
 };
 .EE
 .SH SOURCE
-.B /usr/local/plan9/src/libsec
+.B \*9/src/libsec
 .SH SEE ALSO
 .IR mp (3),
 .IR aes (3),