def first_set
      first = steps[0]

      if first.is_a?(Rule)
        return first.first_set
      elsif first
        return [first]
      else
        return []
      end
    end
def first_set
      first = steps[0]

      if first.is_a?(Rule)
        return first.first_set
      elsif first
        return [first]
      else
        return []
      end
    end
@param [Array] steps
 @param [LL::SourceLine] source_line
 @param [String] ruby_code


 Returns the FIRST() set of this branch.

 @return [Array<LL::Terminal>]