About a year and nine months ago, I poses a question here about Quine's predicate functor logic and ontological nihilism. I'm still having trouble wrapping my head around these ideas. I hope someone here can help me with the following questions:
The first question I have is where I can find a text that teaches predicate functor logic. Everything that I've looked at touches upon first order logic. Articles on ontological nihilism talk about PFL as a language for ontological nihilism but don't get into the mechanics.
MY second question has to do with the nature of "features" in a feature placing language. In my previous question, @Double Knot wrote, "Feature and relation boundary is not clear-cut and both are described as property via function/map in math and predicate in logic (number 2 can be also thought of as a doubling function)." Is this taken to mean that there is not a clear boundary between the idea of features and relations and/or that a feature is similar to the concept of a map in category theory?
Last, is it possible to recover the concept of a number from a feature placing language?