[MODEST] toy model

[Shawn Slavin]

Peter,

> since i just went through modifying 'ancient' software to make it work
> for the current larger computing systems, I just wanted to remind you
> that integers only count to about 2 billion (2**31).

A tiny technical point here:  the 4-byte signed max is (2^{31} - 1),
because of the zero.  It's irrelevant to the discussion here, but people
should be aware of this, if it's ever used as a limit.

Cheers,

Shawn