Green's Open Problems #65

### What is the conjecture
https://people.maths.ox.ac.uk/greenbj/papers/open-problems.pdf#problem.65

Is there $c > 0$ with the following property: whenever $A \subset [N]$ is a set of size $N^{1-c}$, $A - A$ contains a nonzero square? What about $A - A$ containing a prime minus one?

### [AMS categories](https://github.com/google-deepmind/formal-conjectures/labels?q=ams-)

* ams-11
* ams-05

### Choose either option
- [ ] I plan on adding this conjecture to the repository
- [x] This issue is up for grabs: I would like to see this conjecture added by somebody else