fprintf(stderr, "\n*** %s failed", op);
fputs("\n*** a = ", stderr); mp_writefile(a, stderr, 10);
fputs("\n*** b = ", stderr); mp_writefile(b, stderr, 10);
fprintf(stderr, "\n*** %s failed", op);
fputs("\n*** a = ", stderr); mp_writefile(a, stderr, 10);
fputs("\n*** b = ", stderr); mp_writefile(b, stderr, 10);