Nevermore

It's closing time at Chez Dakota, and you're down on your luck as usual, so Skinny offers you one last wager.

"I'll bet you lunch tomorrow that I will provide evidence today that all ravens are black without showing you any ravens."

Obviously Skinny has been reading Poe too much again, but your curiosity wins out. Anyway, you're sure lunch with Skinny will prove entertaining as always. You accept, and Skinny offers you a brown beer bottle. You politely refuse the drink, but Skinny laughs, saying:

"No, no. This is my evidence. As any good logician like yourself knows, the statement 'all ravens are black' is equivalent to the statement 'all non-black things are non-ravens'. Here is a non-black thing, and it's not a raven, so this is evidence that all ravens are indeed black, though admittedly a very small piece of evidence."

Perhaps you need that drink after all. Has Skinny won again?