sorting a list and counting interchanges

[Bill Mill]

<snip>
> 
> I think it's harder for some people to see why the
> 
>     assert j not in seen
> 
> must be true, although that's obvious after just a few hours' thought <wink>.

That's where you get to leave comments like:

#it follows logically that
assert j not in seen

or

#by implication
assert j not in seen

just to really frustrate the guy reading your code.

Peace
Bill Mill
bill.mill at gmail.com