Chess board a b c de f g h 8 坚 8 For a particular set of 7 X 7 forbidden positions 6 ☒ 6 5 X 5 4 × 4 Bc[ml×[m 3 ☒ 2 ☒ 2 Tk· X 1 a b d e f g h of ways of placing k non-attacking rooks in B No the of placements of n non-attacking rooks?Chess board B ⇥ [n] ￾ [n] For a particular set of forbidden positions the # of placements of n non-attacking rooks? N0 : rk : # of ways of placing k non-attacking rooks in B