Can someone explain me how I read that sum notation? I have that task: $$n\in \mathbb{N}^* \quad and \quad A_1...A_n \quad are\ finite\ groups $$ $$ \#(\cup_{i=1} ^{n} A_i)=\sum_{I \subseteq[n], I\neq \emptyset}(-1)^{( \#I)}\#( \cap_{i\in I}A_i) $$ The thing that i don't understand is how to read it when the sum doesn't have limit.
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https://en.wikipedia.org/wiki/Inclusion–exclusion_principle – user940347 Nov 07 '21 at 22:13
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What does # signify in the expression? – herb steinberg Nov 07 '21 at 22:20
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1The sum ranges over all non-empty sets $I$, which are a subset of $[n]$ – Andreas Lenz Nov 07 '21 at 22:21
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means the cardinality – MeepMeep Nov 08 '21 at 14:17