python递归意外答案

Question

def gcd(a, b):
    print(a, b)
    if min(a, b) == 1:
        return 1
    else:
        if (min(a, b) % min(a, b) == 0) and (max(a, b) % min(a, b) == 0):
                print('else: ', min(a, b))
                return min(a, b)
        gcd(min(a, b)-1, max(a, b))

为什么上面的代码没有为gcd（9,12）返回6？这就是我得到的：

gcd(6,12)
6 12
else:  6
Out[98]: 6

gcd(9,12)
9 12
8 12
7 12
6 12
else:  6