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1. The problem statement, all variables and given/known data

The exercise is to prove the following statements.

Suppose that [itex]f:X \rightarrow Y[/itex], the following statement is true.

If [itex]\{G_{\alpha} : \alpha \in A\}[/itex] is an indexed family of subsets of Y, then [itex]f^{-1}(\bigcup_{\alpha \in A} G_\alpha) =\bigcup_{\alpha \in A} f^{-1}( G_\alpha) [/itex].

2. Relevant equations

The relevant information in this case is the definitions. In this case I need to know what the definition of an inverse function is.

DEF: Suppose [itex]f:X \rightarrow Y[/itex] and [itex] A \subset Y[/itex]. [itex]f^{-1}(A) = \{x \in X: f(x) \in A\}[/itex]

3. The attempt at a solution

The solution I've been looking thus far is a point wise argument.

Choose [itex]t \in f^{-1}(\bigcup_{\alpha \in A} G_\alpha)[/itex]. So by definition we know

[itex]t \in \{x \in X: f(x) \in (\bigcup_{\alpha \in A} G_\alpha)\}[/itex]. And here is where I'm kind of stuck. I need to some how get my chosen element to be in the other set, therefore making the one set a subset of the other. Then complete the converse of the argument to finish the proof.

Any ideas on where I should be looking, or what I should be thinking about here?

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# Homework Help: Some set proofs

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