fibonacci :: Int -> Int
-- testing 8 combinations of argument values
-- looking through 2 candidates of size 1
-- looking through 2 candidates of size 2
-- looking through 6 candidates of size 3
-- looking through 1 candidates of size 4
-- looking through 11 candidates of size 5
-- looking through 5 candidates of size 6
-- looking through 27 candidates of size 7
-- looking through 20 candidates of size 8
-- looking through 95 candidates of size 9
-- looking through 148 candidates of size 10
-- looking through 431 candidates of size 11
-- looking through 925 candidates of size 12
-- looking through 2377 candidates of size 13
fibonacci n  =  if n <= 1 then 1 else fibonacci (dec n) + fibonacci (dec (dec n))