Reader DM sends in a link for the for the misnegation archives — Evan Ackerman, "NASA: Warp drive is 'plausible and worth further investigation'", DVice 9/17/2012:
Warp drive, a staple of science-fiction, has just been deemed "plausible and worth further investigation" by the smart and apparently not crazy people over at NASA. And by way of further investigation, they've gone and started trying to create warp bubbles in the lab. [...]
All you have to do to travel faster than light is to create a warp field with a ring of exotic matter, encasing your ship in a separate bubble of space, and then get the space to move faster than the speed of light. Technically, since it's the fabric of space that's moving, nothing in space itself is breaking the light speed limit. It's a loophole, yes, but it works. Or at least, we're not sure that it doesn't not work.
Talking about starships in the context "we're not sure that __" licenses pretty much any number of layers of negation: "We're not sure that it doesn't not fail to work", "We're not sure that it doesn't not fail to not work", etc., are presumably all true as well, for most values of "we".
But DM is pretty sure that it would have been OK to stop at
… but it works. Or at least, we're not sure that it doesn't work.
At least, he's not sure that it wouldn't have been OK not to not stop there.