List s1 = Arrays.asList(1, 2);
List s2 = Arrays.asList(1, 3);
 
s1.stream()
  .flatMap(v1 -> s2.stream()
                   .filter(v2 -> Objects.equals(v1, v2))
                   .map(v2 -> tuple(v1, v2)))
  .forEach(System.out::println);