Is the function of "but" in the sentences below a preposition, please?
If so, what's the exact rule on the case? That is, what part of speech is used after it, a bare infinitive, a full-infinitive, an adjective, a noun or what?
We've had nothing but trouble with this car.
The problem is anything but easy.
I don't intend to do anything but to wait for news.
He does nothing but eat.