- #1
Esran
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Homework Statement
I know this is probably fairly trivial, but for the life of me I cannot remember or reconstruct the proof for the proposition, "The sum of the lengths of a finite number of overlapping open intervals is greater than the length of their union."
Homework Equations
Not Applicable.
The Attempt at a Solution
Suppose [tex]G=\left\{\left(a_{i},b_{i}\right)\right\}^{n}_{i=1}[/tex] is a finite collection of overlapping open intervals (any two intervals in [tex]G[/tex] have nonempty intersection). We wish to show:
[tex]b_{n}-a_{1}\leq\sum^{n}_{i=1}\left(b_{i}-a_{i}\right)[/tex].
My current approach is the following:
[tex]\sum^{n}_{i=1}\left(b_{i}-a_{i}\right)=b_{n}-a_{1}+\left(b_{n-1}+b_{n-2}+\ldots+b_{1}\right)-\left(a_{n}+a_{n-1}+\ldots+a_{2}\right)[/tex]
It remains to show that [tex]\left(b_{n-1}+b_{n-2}+\ldots+b_{1}\right)-\left(a_{n}+a_{n-1}+\ldots+a_{2}\right)[/tex] is a positive number.
Well, we know [tex]\left(b_{n-1}+b_{n-2}+\ldots+b_{2}\right)-\left(a_{n-1}+a_{n-2}+\ldots+a_{2}\right)[/tex] is a positive number, so we just need to establish that [tex]b_{1}-a_{n}<\left(b_{n-1}+b_{n-2}+\ldots+b_{2}\right)-\left(a_{n-1}+a_{n-2}+\ldots+a_{2}\right)[/tex].
This is where I am having problems.