Thread: Proofs. Need help proving the following

Can anyone prove this?If S is a subset of D(f) then S is a subset of f^(-1)(f(S))

So far I have:
Let x be an element of S
Therefore, f(x) is an element of f(s)
f inverse of f(s) = {p is an element of D(f) | f(p) is an element of f(s)}
since f(x) is an element of f(s), then x is an element of f inverse f(s)

Anything else I can add or omit?
Any help is very much appreciated!

Originally Posted by duckyone

[COLOR=#373737][FONT=Lucida Grande]Can anyone prove this?If S is a subset of D(f) then S is a subset of f^(-1)(f(S))

It is hard for to read your question. But I think it means:
If and then .

The definition gives us implies .

Can you finish?