Hi all,

I was writing a solution for this problem and while checking if it was right I've found this one on Penrose's home page:

http://www.roadsolutions.ox.ac.uk/solut ... ution2.jpgCan I kindly ask you why:

Mainly what's not so clear to me is the fraction

, could you please explain me why this equation holds?

For those interested there's another published solution:

http://downroadtoreality.blogspot.com/2 ... se-24.html that's IMHO more elegant than the first one, even if it's less clear.

Thanks for your help!