Economics books for the mathematician?

[PhDorBust]

I thinking about switching from math to econ for grad school, and was wondering how mathematical is upper level economics?

I have trouble reading textbooks that don't follow the theorem->proof outline. I've found Mas-Colell gives a nice mathematical treatment of microeconomics. Any other economics gem for the mathematician?

 

[qspeechc]

Check out this thread where I asked a similar question:
https://www.physicsforums.com/showthread.php?t=505320