Re:

#include <stdio.h>
int f1 (int x4, int x3, int x2, int x1) {
    return ((!x4 \&amp;\&amp; x3 \&amp;\&amp; !x2 \&amp;\&amp; x1) || (!x4 \&amp;\&amp; x3 \&amp;\&amp; x2 \&amp;\&amp; x1) || (x4 \&amp;\&amp; !x3 \&amp;\&amp; !x2 \&amp;\&amp; x1) || (x4 \&amp;\&amp; !x3 \&amp;\&amp; x2 \&amp;\&amp; x1) || (x4 \&amp;\&amp; x3 \&amp;\&amp; !x2 \&amp;\&amp; x1)  || (x4 \&amp;\&amp; x3 \&amp;\&amp; x2 \&amp;\&amp; !x1) | (x4 \&amp;\&amp; x3 \&amp;\&amp; x2 \&amp;\&amp; x1));
}
int f2 (int x4, int x3, int x2, int x1) {
    return ((x3 \&amp;\&amp; x1) || (x4 \&amp;\&amp; x1) || (x4 \&amp;\&amp; x3 \&amp;\&amp; x2));
}
int main (void) {
    int x1;
    int x2;
    int x3;
    int x4;
    for (x4 = 0;  x4 < 2; x4++) {
        for (x3 = 0;  x3 < 2;  x3++) {
            for (x2 = 0;  x2 < 2;  x2++) {
                for (x1 = 0;  x1 < 2;  x1++) {
                    printf ("%i %i %i %i | %i %in", x4, x3, x2, x1, f1(x4, x3, x2, x1), f2(x4, x3, x2, x1));
                }
            }
        }
    }
}