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I don't know how to write it in $\LaTeX.$ It is a tall skinny bold C. This is the context: A set is defined by: The formula

where $\complement\atop{\smash \scriptstyle i}$ is the thing I don't understand. The $i$ is actually directly underneath the weird $C$ in this case. Can anyone explain what this means?

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    (I deleted a comment earlier which referred to a now-deceased link)2012-09-27

1 Answers 1

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It's the coefficient operator. It extracts the ith coefficient of the Taylor expansion. This is used a lot in combinatorics with generating functions.

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    They don't. In fact the second edition of Stanley (http://www-math.mit.edu/~rstan/ec/ec1/) uses the $[z^n] f(z)$ notation (see p. 11).2016-02-08