code: @SuppressWarnings("JavaDoc")
      public static <_1, _2> Tuple2<_1, _2> tuple(_1 _1, _2 _2) {
          return singletonHList(_2).cons(_1);
      }
docs: Static factory method for creating a 2-element HList.
  
  @param _1   the head element
  @param _2   the second element
  @param <_1> the head element type
  @param <_2> the second element type
  @return the 2-element HList
  @see Tuple2