Sorting Without Comparison

1. You are given two numbers (a, b) and you wish to assign one each to (A, B) such that A<=B. That is, you want A to equal the minimum of a and b, and B to equal the maximum of a and b. How can you write A=f(a,b), and B=g(a,b,A) to correctly assign the values? Try to make functions f and g as simple as possible.
2. Can you extend the above result for three original numbers (a, b, and c) to be assigned to A<=B<=C?
3. Can you extend it to four numbers simply?
4. Is there a general approach for more numbers, or is a repetitive method required?