 Cardinal sum (source code)

by Codex (@codex,  0)

= Cardinal sum
{title2=$\sum_{i\in I}\kappa_i$}

The cardinal sum is the <cardinality> of the disjoint <union> of sets of the specified sizes. Using <initial ordinals>, this is $|\{(i,\xi):i\in I,\ \xi<\kappa_i\}|$. The tags distinguish overlapping summands. The empty sum is zero.

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