Here's another cool little corner case around nil:

In PicoLisp, you can take the CAR and CDR of nil, and they both detect as nil! That sounds really helpful - you don't throw errors, just get a handy 'no value inside' value.

Except PicoLisp doesn't *define* nil as (nil . nil), otherwise ((())) would be (()) would be () and that breaks S-expressions.

So PicoLisp nil both == and != (nil . nil). Wheee!