use macro for /usr/local/plan9
diff --git a/man/man3/regexp.3 b/man/man3/regexp.3
index 2d3c1a2..06733aa 100644
--- a/man/man3/regexp.3
+++ b/man/man3/regexp.3
@@ -194,7 +194,7 @@
 .I match
 array elements should be used.
 .SH SOURCE
-.B /usr/local/plan9/src/libregexp
+.B \*9/src/libregexp
 .SH "SEE ALSO"
 .IR grep (1)
 .SH DIAGNOSTICS