let board = [|
('a', 1); ('b', 2); ('c', 3); ('d', 4);
('e', 5); ('f', 6); ('g', 7); ('h', 8)
|];;

(*** 1 ***)
let int_of_col = fun x ->
	match x with
	| 'a' -> 1
	| 'b' -> 2
	| 'c' -> 3
	| 'd' -> 4
	| 'e' -> 5
	| 'f' -> 6
	| 'g' -> 7
	| 'h' -> 8;;

(*** 2 ***)
let attack = fun (k,b) (l,d) ->
	if int_of_col k == int_of_col l && b == d then
		false
	else	if abs(int_of_col k - int_of_col l) * abs(b - d) == 0
	|| abs(int_of_col k - int_of_col l) == abs(b - d)
	then
		true
	else
		false;;


(*** 3 ***)
let attacked = fun array ->
	let war = [|false; false; false; false; false; false; false; false|] in
		for i = 0 to (Array.length array)-1 do
			for j = 0 to (Array.length array)-1 do
				if attack (array.(i)) (array.(j)) then
					(war.(i) <- true;
					war.(j) <- true;);
			done
		done;
		war;;


(*** 4 ***)
let checkIfTrue = fun state ->
	if state then
		false
	else
		true;;

let safe = fun s ->
	Array.for_all checkIfTrue (attacked s);;

safe [|('a', 7); ('b', 2); ('d', 3);
('e', 6); ('f', 8); ('g', 5); ('h', 1)|];;