Why doesn't the recursive function work?

Question

Python

I can't figure out why the code below is not working. The idea is this: there is a limit from 1 to 11, to the number from [1, 11] we add a number not from the range, but as soon as we reach the extreme limit, we continue to add from the number on which the limit begins.
For example: the range is from 1 to 3, we add 4 to 2 and get 3. (i.e. 2+(1)=3, 3+(1)=1, 1+(1)=2, 2 +(1 ) = 3.

def ab(a,b):
    rangA = 1
    rangB = 11
    ans = a+b
    if ans <= rangB:
        return ans
    else:
        c = b - (rangB-a)
        a = 0
        ab(a,c)

Answer 1

In the recursion call, in the last line, shouldn't it be like this:
?

Answer 2

A small offtopic, but suddenly come in handy.
Here you can do without recursion. Operations in the residue ring are performed modulo the base, i.e. the result is the remainder of the division (in your case by 11). But this will give us the range [0,10] since the remainder of dividing 11 by 11 is 0. But 0 and 11 belong to the same class of residues (they have the same remainders when divided by the base), which means they are equivalent, and we can replace one with the other, thereby obtaining the range [11, 1..10 ]:

z = 11 #основание
def ab(a,b):
    res = (a + b) % z
    if res == 0:
        return z
    else:
        return res