<Ayuh.  It's a head-bender, so solve it graphically.  Wrap two paper
> slips around the ends of a pencil, use one hand to drive it and the
> other to resist, mark arrows on each in the direction of the force
> your hand is exerting.
>
> Flip the pencil end-for-end -- no change.  Use your other hand to
> drive the pencil (with or without flipping it -- now you're working
> against the arrows, so swapping side-to-side works if you can.  Now
> flip the paper slips around on the pencil -- now you're pushing with
> the arrows again, so that works too.
>
> So...end-for-end does nothing.  Flipping the joints on the shaft and
> replacing it on same side works.  Swapping the shaft to the other
> side works.  Flipping joints *and* swapping to the other side negates
> the effect.
>
> :-)
> d
> >
> --
> David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
> '84 Westy "Dutiful Passage," '85 GL "Poor Relation"
>

Defininitely a STAR.  Even I can understand that. I think a tire
rotation(bi-directional) is a good analogy also.

--
Michael in San Antonio
91GL AT 'Gringo'