use macro for /usr/local/plan9
diff --git a/man/man1/core.1 b/man/man1/core.1
index 3c2c0d4..c051386 100644
--- a/man/man1/core.1
+++ b/man/man1/core.1
@@ -39,7 +39,7 @@
 .I core
 searches the current directory.
 .SH SOURCE
-.B /usr/local/plan9/src/cmd/core.c
+.B \*9/src/cmd/core.c
 .SH "SEE ALSO
 .IR acid (1),
 .IR db (1),