Originally Posted by

**davidciprut** So I uploaded a picture that is written a claim that I didnt understand. This is the way that is written in my notebook and I didnt understand why its not a field. So from what I have been told that it is not field because some numbers in Zn their inverse. But how is this proof , proving that exactly? And I wanted to ask that if this is a contradiction to the uniqueness of 0? I mean in multiplication only when we multiply with zero we get zero but here we didnt multiply with zero is that contradiction to that? thank you