code: public boolean contains(int left, int right) {
          if (line[left] == null) {
              return false;
          }
          return line[left].contains(right);
      }
docs: Element test.
  @param  left  left value of the pair to test.
  @param  right right value of the pair to test.
  @return  true, if (left, right) is element of the relation.