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SithsNGiggles
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Homework Statement
The question is "Prove
[itex]f(\bigcap_{\alpha \in \Omega} A_\alpha) \subseteq \bigcap_{\alpha \in \Omega} f(A_\alpha)[/itex]
where [itex]f:X \rightarrow Y[/itex] and [itex]\{A_\alpha : \alpha \in \Omega\}[/itex] is a collection of subsets of [itex]X[/itex].
Also, prove the statement's equality when [itex]f[/itex] is an injective function.
Homework Equations
The Attempt at a Solution
Let [itex]f(x) \in f(\bigcap_{\alpha \in \Omega} A_\alpha)[/itex].
Then [itex]\exists x \in \bigcap_{\alpha \in \Omega} A_\alpha[/itex],
i.e. [itex]\exists x \in A_\alpha \forall \alpha \in \Omega[/itex].
It follows that [itex]\exists f(x) \in f(A_\alpha) \forall \alpha \in \Omega[/itex],
i.e. [itex]f(x) \in \bigcap_{\alpha \in \Omega} f(A_\alpha)[/itex].
Thus [itex]f(x) \in f(\bigcap_{\alpha \in \Omega} A_\alpha) \Rightarrow f(x) \in \bigcap_{\alpha \in \Omega} f(A_\alpha)[/itex], and hence,
[itex]f(\bigcap_{\alpha \in \Omega} A_\alpha) \subseteq \bigcap_{\alpha \in \Omega} f(A_\alpha)[/itex].
I tried following a similar thought process in proving the reverse, but I end up showing that the RHS is a subset of the LHS. Although it works out for the injective f, where does it go wrong when f is not injective?