use macro for /usr/local/plan9
diff --git a/man/man3/mouse.3 b/man/man3/mouse.3
index 8d2eca2..216c72b 100644
--- a/man/man3/mouse.3
+++ b/man/man3/mouse.3
@@ -240,7 +240,7 @@
 restoring the display when the menu is removed.
 .PP
 .SH SOURCE
-.B /usr/local/plan9/src/libdraw
+.B \*9/src/libdraw
 .SH SEE ALSO
 .IR graphics (3),
 .IR draw (3),