# If G is cyclic, and G is isomorphic to G', then G' is cycli

1. Feb 20, 2017

### Mr Davis 97

1. The problem statement, all variables and given/known data
Title

2. Relevant equations

3. The attempt at a solution
This would seem to be very easy problem, since it's intuitively obvious that if two groups are isomorphic, and one is cyclic, then the other is cyclic too. However, I can't seem to formalize it with math.

Here is an idea. We can define that a group is cyclic by saying that for all b in G, there exists an a such that $a^n = b$ for some integer n. Now if G is cyclic, and we have an isomorphism $\phi$ from G to G', then it is true that $\phi (a) ^n = \phi (b) = b'$, which means that G' is also cyclic. Does this sketch of a proof the right idea?

2. Feb 20, 2017

### Staff: Mentor

Yes it is. You can leave out the $b's$ as you don't need them, the generator $a$ is sufficient, i.e. simply write $a^n$. It doesn't need to be named. And you may forget the isomorphism, surjectivity is sufficient. And subgroups of cyclic groups are also cyclic.