Usefulness of the "not in" operator

[rusi]

On Oct 8, 6:31 pm, Roy Smith <r... at panix.com> wrote:
> In article <87ehyn8xlp.... at dpt-info.u-strasbg.fr>,
>  Alain Ketterlin <al... at dpt-info.u-strasbg.fr> wrote:
>
> > Sure, but note that you can also reformulate != using not and ==, <
> > using not and >=, etc. Operators like "not in" and "is not" should
> > really be considered single tokens, even though they seem to use "not".
> > And I think they are really convenient.
>
> If you want to take it one step further, all the boolean operators can
> be derived from nand (the dualists would insist on using nor).
                        ^^^^^^^^^^^^
????