Usefulness of the "not in" operator

[Chris Angelico]

On Tue, Oct 11, 2011 at 7:28 PM, Nobody <nobody at nowhere.com> wrote:
> It's useful insofar as it allows you to define "numbers" given nothing
> other than abstraction and application, which are the only operations
> available in the lambda calculus.
>

Heh. This is why mathematicians ALWAYS make use of previously-defined
objects! In pure lambda calculus, constants are even more painful than
in SPL[1]...

ChrisA
[1] http://shakespearelang.sourceforge.net/report/shakespeare/shakespeare.html#SECTION00045000000000000000