Is there a good example of how toupper() works?

[pgd at bbt.se]

In article <18575 at haddock.ima.isc.com> karl at ima.isc.com (Karl Heuer) writes:
>
>ANSI C.  My personal ansi/ctype.h is:
>	#include "/usr//include/ctype.h"
>	#undef tolower
>	#undef toupper
...

Is there some special benefit of saying "/usr//include" instead of
					     ^^
"/usr/include"?