- #1

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## Homework Statement

Show that ##\langle \mathbb{R}_{2 \pi}, +_{2 \pi} \rangle## is not isomorphic to ##\langle \mathbb{R}, +\rangle##

## Homework Equations

## The Attempt at a Solution

I know how to show that two groups are isomorphic: by finding an isomorphism between them. However, I am not sure how to show that there does not exist an isomorphism at all.