2c

Write the following function in OCAML

(c) Implement a recursive OCaml function tetra2 : int -> int, which computes the nth Tetranacci number in time linear in n, i.e. it computes Tn by making one recursive call (instead of 4 recursive calls as it was for function tetra1 in Problem 1). Put differently, the number of recursive calls that tetra2 makes is linear in n.