let ll1 = string_of_int (List.length l1) in
let ll2 = string_of_int (List.length l2) in
let diff = string_of_float (after -. before) in
let ll1 = string_of_int (List.length l1) in
let ll2 = string_of_int (List.length l2) in
let diff = string_of_float (after -. before) in