Synthesized answer
The provided passages do not contain information that answers the question about what questions remain unanswered in "Principia Metaphysica (with Bernard Linsky)." The passages are titled "Procedures and Metaphysics" by Edward William Strong and are categorized under Mathematics [1]. This suggests the content is related to philosophical procedures and metaphysical concepts within mathematics, but it does not explicitly list or discuss unanswered questions from any specific work.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: Procedures and Metaphysics by Edward William Strong Categories: Mathematics