I was formerly an economics major and now also majoring in mathematics. I want a textbook that is rigorously based on mathematics; not just using mathematcis whenever the author wants, but in a more unified way to explain a concept. I've learned enough mathematics in undergraduate level so mathematics will hardly be a problem. I've searched for information, but I really wanted textbooks that satisfy this specific condition; explaining concepts with sound mathematics in a unified way.
Any help will be grateful.