- #1
happysauce
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Homework Statement
I just have a question about the integral of a product space. How do I define the integral of product spaces in terms of characteristic functions?
What I mean by that is, if I have a measure space, (X,M,u) and f(x) is a positive, simple, measurable function. Then ∫f du = Ʃa[itex]_{i}[/itex]u(E[itex]_{i}[/itex]). What I want to know is how can I apply this to a simple function given the product space of (X,M,u) and (Y,N,v)?
The problem I have to do is to prove that ∫f(x)g(y)d(u×v)=(∫f(x)du)(∫g(y)dv), you can't use fubini's theorem since the problem doesn't assume the measure spaces are sigma finite and the hint suggested using standard limit theorems for integrals, which made me think I probably had to use simple functions...