Recursion in erlang (Fibonacci, factorial, n dimensions)

recursion.erl

-module(recursion).

-export([fac/1,fib/1,cut/1]).

fac(0) -> 
    1;
fac(N) when N>0 ->
    fac(N-1) * N;
fac(N) when N<0 ->
    io:fwrite("Postieve number please", []).

fib(0) -> 0; 
fib(1) -> 1; 
fib(N) when N>0 -> 
fib(N-1)+fib(N-2).

cut(0) -> 1; 
cut(1) -> 2; 
cut(N) when N>0 -> 
cut(N-1)+N.