Choose the right license for an Android App (no modification)
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I've finished (almost) an Android app for my University and they want to buy it, the problem is that they can adapt it and resell it to other university.

How can I protect my work from this?

I wish to sell them my app, let them make some little modification (for example in some xml files if they change server or something like this) but I don't want them to sell my app to others. Do I have to close the source?

Is there some Licence that can I use for this?
Should I specify somewhere "just for 'My University'"?

Do I have to care about any Android licence (I haven't done anything strange with the standard Android code).

(sorry but it's my first selling work...)