Stats proof

[stray cipher]

On the second page of this proof, why can we switch the summation from j=1 to n to the summation from i=1 to n? (The second step on the second page)

[lone lintel]

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[nimble vessel]

What you call the summation variable doesn't matter, so you can change it as you want.

[stray cipher]

So could I have done this earlier on in proof and it wouldn't have been a problem?

[nimble vessel]

Ah, but note that you can only do that for a single sum. Of course, you can't make two variables in a double sum the same.

[stray cipher]

Oh yes of course, thanks I understand

[tranquil fiber]

@stray cipher has given 1 rep to @nimble vessel