fun remove(original, final, n, i) = if null original then final
                                else if i = n then remove(tl(original), final, n, i+1)
                                else remove(tl(original), final @[hd(original)],n,i+1);

fun rem k list = remove(list, [], k, 1);

fun det(list) =  let val a = hd(list);
                 val b = hd(tl(list));
                 val c = hd(a);
                 val d = hd(tl(a));
                 val e = hd(b);
                 val f = hd(tl(b)); in

                 c*f - d*e end;


fun operate(a,b,i)= if a=b then a-b else a+b;

fun compute(matrix,list,ans,i) = if null list then ans
                            else compute(matrix,tl(list), operate(ans, hd(list)*det(map (rem i) (tl(matrix))), i), i+1);
fun value(matrix) = compute(matrix,  hd(matrix), 0, 1);