Comparing f(x) and g(x): Analyzing the Possibilities

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SUMMARY

The discussion focuses on the relationship between two measurable functions, f(x) and g(x), and the conditions under which they can be considered equal almost everywhere. It establishes that the sets E_1 and E_2, defined as the regions where f(x) is less than g(x) and vice versa, are measurable. The conclusion drawn is that if the integrals of the differences over these sets are zero, then the measure of their union must also be zero, leading to the conclusion that f(x) equals g(x) almost everywhere.

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jdinatale
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I feel like I got the first part, but the converse is a little tricky. I'm not sure if I am allowed to conclude at the end that f(x) must equal g(x) almost everywhere.

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Your argument for the converse does not work. Notice that since f,g are measurable it follows that the sets E_1 = \{x \in X:f(x) < g(x)\} and E_2 = \{x \in X:g(x) < f(x)\} are measurable. Now use the fact that \int_{E_1} f-g = 0 and \int_{E_2} f-g = 0 to prove that \mu(E_1 \cup E_2) = 0.
 

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