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/* h1.h */

#ifndef H1_H
#define H1_H
...

#ifndef COUNT_T
#define COUNT_T
typedef unsigned int count;
#endif

...
#endif
/* h2.h */

#ifndef H2_H
#define H2_H
...

#ifndef COUNT_T
#define COUNT_T
typedef unsigned int count;
#endif

...
#endif

#include "h1.h"           /* count defined */
#include "h2.h"           /* count not redefined */