def skip( index, start )
      if @index == index
        Lookup.new @p.lookup( start, @stride ), @index, @stride
      else
        Lookup.new @p.skip( index, start ), @index, @stride
      end
    end
def skip( index, start )
      if @index == index
        Lookup.new @p.lookup( start, @stride ), @index, @stride
      else
        Lookup.new @p.skip( index, start ), @index, @stride
      end
    end
Skip elements of an array

 @param [Variable] index Variable identifying index of array.
 @param [Node] start Wrapped integer with number of elements to skip.

 @return [Node] Lookup object with elements skipped.

 @private