> I'm sorry Unca Joel, that was a good effort but you didn't look at
> page 80.11.
> The apologies should go to MC Escher.

actually, i did look ... but Escher never wrote no songs. ;)

... and yes, that 80.11 drawing really IS the way the ventilation
system works.
if you've ever driven in a non-airconditioned 1980 vanagon, you'd know
that 80.11 depicts the path of the ventilation air (so called)
perfectly: you can't get no satisfaction! ;)

unca joel