#include <reg51.h>

main( void ) {
    char a, b, c, d;
    char i;

    for( i = 0; i < 8; i++ ) {
        a = i & 0x01;
        b = i & 0x02;
        c = i & 0x04;
        d = i - 4;
			  P0 = ( a != d ) || ( b > c ) && ( d < b );
    }
    while( 1 );
}