word choice

[joyquality]

There are two events, Event A and Event B.

If Event B can only occur if Event A has already happened, I can say Event B requires Event A.
If Event B can only occur if Event A has NOT happened, Event B _________ Event A.
Is there a one-word verb in English that can go in that slot? Everything I can think of only fits the Event A ________ Event B

Comments

This is hard.

[keystricken]

What about "disproves"? It's not perfect, but it's the best thing I've got.

Re: This is hard.

[keystricken]

Or maybe "contradicts" is better.

[nplusm]

Well, none of these are perfect, but "denies" is almost right.

Event B denies Event A?
Event B disallows Event A?

[flamingweasel]

I think these are backwards from what K wants: event b is denied by event a. This is hard; I suggested precludes, which is wrong in the same way. "Precluded by" is close, but multiword. Jes's disrequires is good (and something that came to mind) except it's not actually a word.

It should be, though.

[jes5199]

I use the word "disrequires" when I need to say that, but other people rarely understand what I mean.

[creases]

The closest I can think of is "obviate", which means that Event B makes it so that Event A doesn't have to happen.

[conform]

I think the ideal verb for the relationship here is "precludes", but I agree with Ryan that there's probably not a shorter form than "is precluded by". Which doesn't surprise me.