#include <stdio.h>

int is_reverse(const char * s1, const char * s2) {
    const char * r2 = s2;
    while (*r2 != 0)
	++r2;

    while (r2 != s2 && *s1 != 0) {
	--r2;
	if (*r2 != *s1)
	    return 0;
	++s1;
    }
    return (r2 == s2 && *s1 == 0);
}

int main(int argc, const char * argv[]) {
    for(int i = 1; i < argc; ++i)
	for (int j = i + 1; j < argc; ++j)
	    if (is_reverse(argv[i], argv[j]))
		printf("%s %s\n", argv[i], argv[j]);
}