Let's assume that
Article 50 is invoked and UK officially leaves EU
For some reason, both UK populace (a large share) and enough powers that be or popular will in EU, decide that UK ought to re-join EU, 1,2 or 5 years down the road.
So far I heard tons of people asserting that this cannot happen, that you can't re-enter EU. But none of them backed it up with any facts.
So... are there actual rules/laws in place that would prevent UK from re-joining EU, if both sides are willing/interested?
If the assertion is incorrect, what are the minimal requirements for that to happen?
(I can split #2 into a separate question if it makes this question too broad)