Computer science: Functions help

Hi, I hope I can get some help with this problem. The class is called "Formal models of computation". It's a computer science course where we talk about models of how computers work, Turing machines, automatons, etc. It's kind of like Discrete Math for computer science (which I hated).

Give functions f: E -> E (where E is the set of even integers) that fulfill the following properties

a. f is one-to-one, but not onto or total

b. f is total, but not one-to-one or onto

c. f is total, one-to-one and onto, but is not the identity function (f(x) = x)

d. f is not total or one-to-one, but is onto.

I have part c figured out but can't come up with anything for the other 3. Everytime I come up with a function for one property it doesn't meet the other ones. The professor wants the functions to be in the form f(x) = something. We are not allowed to create subsets of set E either. The functions have to work over the entire set E.

Thanks for any help.