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This category contains definitions related to Summations.
Related results can be found in Category:Summations.

Let $R \left({j}\right)$ be a propositional function of $j$.

Then we can write the summation as:

$\displaystyle \sum_{R \left({j}\right)} a_j = \text{ The sum of all $a_j$ such that $R \left({j}\right)$ holds}$.

If more than one propositional function is written under the summation sign, they must all hold.