--- self < other
--- self <= other
--- self > other
--- self >= other

    ӱ黻ҡself  other λ¹Ǥ
    self < other Ωޤ

    ƻҴطˤʤ饹ƱΤӤǤϤδط false ֤ޤ
    other 饹⥸塼Ǥʤ㳰 TypeError 
    ȯޤ

        module Foo
        end
        class Bar
          include Foo
        end
        class Baz < Bar
        end
        class Qux
        end
        p Bar < Foo     # => true
        p Baz < Bar     # => true
        p Baz < Foo     # => true
        p Baz < Qux     # => false (version 1.8 Ǥ nil)
        p Baz > Qux     # => false (version 1.8 Ǥ nil)

        p Foo < Object.new # => in `<': compared with non class/module (TypeError)

