# Category theory as a rival

Category theory is a unifying theory of mathematics that was initially developed in the second half of the 20th century. In this respect it is an alternative and complement to set theory. A key theme from the “categorical” point of view is that mathematics requires not only certain kinds of objects (Lie groups, Banach spaces, etc.) but also mappings between them that preserve their structure.

In particular, this clarifies exactly what it means for mathematical objects to be considered to be the same.

— Wikipedia on Unifying theories in mathematics

2010.01.11 Thursday ACHK

# The least of all evils 4

”眾害取其輕”(the least of all evils)這個表達式對我思考(intellectual mind)有很大啟發：有些時候，”邪惡”是必須的，唯有接受。但是 ”接受” 不代表 ”坐以待斃”。反而，我們應努力把邪惡減到最低，即是”眾害取最輕”。

（安：你的重點是，雖然建議要眾害中取最輕(Choose the least of all evils)，但是不能以此為作惡的借口，因為有些時候，evil毋須存在。）

— Me@2010.01.20