fib

fib :: Int -> Integer
fib 0 = 0
fib 1 = 1
fib n = fib (n-1) + fib (n-2)

fib' :: Int -> Integer
fib' n = fst $ sequence !! n -- backslash is similar so stay as lambda function, first element of pair
 where --to !! marks for index
 --relation to , image  of function