The goal is to trace a line with your pencil across each edge on the box only once without crossing the vertices or picking your pencil up.

Note that this "box" contains 16 unique "edges".

Prove why this is an impossible task regardless of where you first place your pencil.

pcbouhid, I don't think the proof is too complex to be commented, and one doesn't necessarily need a theory of graphs to prove it. I believe Erik is correct in his logic, but I agree it might need a little more detail for most to follow.

Otherwise the answer does look good to me.

Posted by Michael Cottle on 2005-04-06 20:47:12