let add_lines ro a b m n =
let a_line_m = a.(ro.(m)) in
let a_line_n = a.(ro.(n)) in
let b_line_m = b.(ro.(m)) in
let b_line_n = b.(ro.(n)) in
for i = 0 to (Array.length a_line_m)-1 do
a_line_m.(i) <- (a_line_m.(i) + a_line_n.(i)) mod 2
done;
for i = 0 to (Array.length b_line_m)-1 do
b_line_m.(i) <- (b_line_m.(i) + b_line_n.(i)) mod 2
done