let rec fib  = function n ->
	if ( n < 0) then raise (Failure "Gunwo")
	else if n = 0 then 0
	else if n = 1 then 1
	else fib (n - 1) + fib (n - 2);;


let fib2 = fun n ->
	let rec fib_tr = fun (n, fib1, fib2) -> 
		if (n < 0) then raise(Failure "Gunwo")  
    else if (n = 0) then fib1 
    else if (n = 1) then fib2
    else fib_tr(n - 1,  fib2, fib1 + fib2)
	in fib_tr(n,0,1);;



let x1 = (-2, -1, 0, 1, 2);;
let (_, _, x, _, _) = x1;; 

let x2 = ((1, 2), (0, 1));;
let ((_, _), (x, _)) = x2;;



let rec initSegment = fun (xs1,xs2) ->
	if (xs1 = []) then true
	else if (xs2 = []) then false
	else if (List.hd xs1 = List.hd xs2) then initSegment(List.tl xs1,List.tl xs2)
	else false;;


let l1 = 1 :: 2 :: [];;
let l2 = 1 :: [];;
initSegment(l2, l1);;

let rec replaceNth = fun (xs, n, el) ->
	if (n < 0 || xs = []) then raise (Failure "Dupa")
  else if (n = 0) then el :: List.tl xs
  else List.hd xs :: replaceNth(List.tl xs,n-1,el);;

replaceNth('a' :: 'b' :: 'c' ::[], 5, 'd')