There are several laws in various countries and states that do not differentiate poker from roulette, but do differentiate chess from roulette. Clearly all three games have a degree of luck involved (white has the edge in chess), but in some the degree is a lot higher than others. Therefore, being able to show that the game is predominantly skill is important.
Those two books:
http://www.amazon.co.uk/s/ref=nb_ss_w_h_...ds=nassim+taleb