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Suppose that $X_1,...,X_n$ are Random Variables and given that there exist an $k$ where k is an integer and $1\le k\le n-1$ s.t. the joint distribution $F_{X_1,...,X_k}$ are independent to $F_{X_k+1,...,X_n}$, prove that for all $1\le r \le k\le m\le n-1$ the joint distribution of $X_1,...,X_r$ is independent to joint distibutions $X_{m+1},...,X_n$

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What did you try? –  Did Oct 4 '12 at 13:54
    
i tried to use contradiction, but not sure how to get the contrary –  Mathematics Oct 4 '12 at 14:04
    
I fail to see how a proof by contradiction would help. More to the point: what is the conclusion you try to reach, that is, what are you trying to prove? –  Did Oct 4 '12 at 16:59
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You could try to use the fact that if $X$ and $Y$ are independent random variables, and if $f$ and $g$ are two (measurable ...) functions, then also $f(X)$ is independent from $g(Y)$.

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but here is about the the joint pmf not pmf of a random variable –  Mathematics Oct 8 '12 at 8:36
    
kjetil: +1. $ $ –  Did Oct 8 '12 at 10:03
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