Hello,
I'm supposed to prove this (f is some function, A is some set):
\(\displaystyle \large f^{-1}(f(A)) \ge A\)
and
\(\displaystyle \large f(f^{-1}(A)) \le A\)
and tell when it is equal (eg. \(\displaystyle \large f(f^{-1}(A)) = A\) )
The second part seems easy, it's equal when f is an injective function, right?
But somehow I can't imagine a situation where it wouldn't be equal... In the first case for example, where does the inequality appear, at f(A), or at f^(-1)(A)? I'd be very grateful for an example.
I'm supposed to prove this (f is some function, A is some set):
\(\displaystyle \large f^{-1}(f(A)) \ge A\)
and
\(\displaystyle \large f(f^{-1}(A)) \le A\)
and tell when it is equal (eg. \(\displaystyle \large f(f^{-1}(A)) = A\) )
The second part seems easy, it's equal when f is an injective function, right?
But somehow I can't imagine a situation where it wouldn't be equal... In the first case for example, where does the inequality appear, at f(A), or at f^(-1)(A)? I'd be very grateful for an example.