The equivalent function 2

Computer Science Level 2

def fun1(a,b):
    if b==0:
        return 0
    return a + fun1(a, b-1)

def fun2(a,b):
    if b==0:
        return 1
   else:
        return fun1(a, fun2(a, b-1))

Which of the following is equivalent to the fun2() function shown above?

Assumptions

$a,b$ are non-negative integers.