Change the order of addition - NISHIO Hirokazu's Scrapbox (Auto-translated from Japanese)

Change the order of addition

associative law : $ (a + b) + c = a + (b + c)

1: $ \sum_i \sum_j f(i, j) = \sum_j \sum_i f(i, j)

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This page is auto-translated from /nishio/足し算の順序の変更. If you looks something interesting but the auto-translated English is not good enough to understand it, feel free to let me know at @nishio_en. I'm very happy to spread my thought to non-Japanese readers.