In mathematics, the regular part of a Laurent series consists of the series of terms with positive powers. ^[1] That is, if

${\displaystyle f(z)=\sum _{n=-\infty }^{\infty }a_{n}(z-c)^{n},}$

then the regular part of this Laurent series is

${\displaystyle \sum _{n=0}^{\infty }a_{n}(z-c)^{n}.}$

In contrast, the series of terms with negative powers is the principal part. ^[1]

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