by stupidityismygam » Sat Mar 27, 2010 1:25 am
Outline:
The paths to the left and the paths up are symmetric so we only need to consider one direction and then double the amount. Consider the paths to the left. Paths either go through one of [unparseable or potentially dangerous latex formula]. So with this you can use the combinatorics counting argument to each of these points (and then to [unparseable or potentially dangerous latex formula]) and then add them all up.
my avatar is pretty awesome
tytia