gistfile1.rb

    class Suit
      def red?; not black?; end
    end

    class Heart < Suit
      def black?; false; end
    end

    class Diamond < Suit
      def black?; false; end
    end

    class Spade < Suit
      def black?; true; end
    end

    class Club < Suit
      def black?; true; end
    end