Synthesized answer
The provided passages do not contain information about what questions remain unanswered in the book "Abstract Objects: An Introduction to Axiomatic Metaphysics" [1]. The passages only state the title and subject categories of the book [1]. Therefore, it is not possible to answer the question about unanswered questions based solely on the given information.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: An Introduction to a Theory of Abstract Objects by Edward N. Zalta Categories: Logic, Symbolic and mathematical Pages: 220