# File lib/facet/interval.rb, line 80
  def initialize(first, last, exclude_first=false, exclude_last=false )
    raise ArgumentError, "bad value for interval" if first.class != last.class
    @first = first
    @last = last
    @exclude_first = exclude_first
    @exclude_last = exclude_last
    @direction = (@last <=> @first)
  end