I am looking for a set of mathematics books to understand proofs in decision theory. Examples would be proofs of utility representations and social choice (im-)possibility results. I found many textbooks on both decision theory and social choice, some of which contain proofs which contain references to mathematical results.
However, I could not find a collection of mathematical results commonly used in these fields. Usual "Mathematics for Economists" textbooks fall short. What is the standard reference/textbook researchers use to find the results they employ?