1 – 4 + 6 – 4 +1

becomes

1 – 1 – 3 + 3 + 3 – 3 – 1 + 1

]]>P.S.: Apologies for messed up math formatting, I should have used LaTeX.

]]>1. If n is odd then there is a simple bijection between even-sized e and odd-sized o subsets, achieved via set complement: e S\o.

2. If n > 0 is even then subsets that do not contain element n have the same bijection as in (1) above, while subsets that do contain n have a slightly different bijection: e S\o U {n}.

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