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!