Lattice diagrams and generator in Algebra

[soopo]

Homework Statement

I do not understand the following statement (Please, see the attachment):

"C4 has trivial subgroups and only one cyclic subgroup of 2 elements, namely <b>. This is because both a and c can be verified to be generators of C4."

The Attempt at a Solution

The notation <something> is normally used to indicate a generator of a group.
However, the paragraph uses the notation only for the cyclic subgroup b such that <b>.

The following support statement for the above clause is what I do not understand:
"This is because both a and c can be verified to be generators of C4."

If a subgroup has a generator, then it is a cyclic group.
The paragraph says that the group has two generators, a and c.
Then, a and c must be also cyclic subgroups of C4.

This is a contradiction to the first clause that C4 has only one generator b.

What does the paragraph really mean?

 

[xepma]

I think they mean is that you can choose either a or c as the generator of the group. You only need one generator, and both elements are candidates for it.

 

[soopo]

I think they mean is that you can choose either a or c as the generator of the group. You only need one generator, and both elements are candidates for it.

Thank you for your answer!

Do you mean that a and c are subgroups of b?
It seems that if a subgroup has two elements, then these two elements are subgroups too.

If they are subgroups of b and b is a generator, then a and c seems to get the "generator" property from b.