I don't know what kind of a 'citation' you're looking for. It's possible to write language like that into a license for use; whether or not that's enforceable is a function of several variables, such as how the license is written, which jurisdiction we're talking about, and which legal authority happens to comment on it. Say I provide some lawyer or judge who confirms this, and you find another who disagrees. There's no conflict there; my whole point is that this is a matter of legal opinion, and therefore a possibility.

Contrast to sale of a physical good, where the first-sale doctrine means that such restrictions on subsequent sale and use can't exist. (The implication is that the same would apply to DRM-free media, because a lack of DRM means that they can't enforce any such restrictions, either through practical means or through legal channels).

This is a pretty easy one. EULAs are generally public information linked to on the internet.

Just link to the EULA that contains language that may indicate you need to delete your ebooks on declaring bankrupcy.

If its 50 pages long, it might be helpful to provide a quote or two. Or link to someone elese who has done that analysis like say groklaw.

So what I'm hearing is that you basically made this up.

>It's possible to write language like that into a license for use

It's possible to write anything into the license. An MP3 license agreement could say that you have to eat a pound of chalk every time you play the song. That doesn't make it legally enforceable.

Your hypothetical "bankruptcy clause" seems like it fits in this same category. Why would a judge ever agree that this is enforceable when it's so pointless and arbitrary?