ideal inverting in Pr\"ufer ringIdealInvertingInPruferRing2004-08-15 15:24:552008-09-22 19:10:18TheoremPr\"ufer ring% this is the default PlanetMath preamble. as your knowledge
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\newtheorem*{thmplain}{Theorem}\begin{thmplain}
\, Let\, $\mathfrak{a}_1$, \ldots, $\mathfrak{a}_n$\, be invertible fractional ideals of a Pr\"ufer ring.\, Then also their sum and intersection are invertible, and the inverse ideals of these are obtained by the formulae resembling de Morgan's laws:
$$(\mathfrak{a}_1+\cdots+\mathfrak{a}_n)^{-1} =
\mathfrak{a}_1^{-1}\cap\cdots\cap\mathfrak{a}_n^{-1}$$
$$(\mathfrak{a}_1\cap\cdots\cap\mathfrak{a}_n)^{-1} =
\mathfrak{a}_1^{-1}+\cdots+\mathfrak{a}_n^{-1}
$$
\end{thmplain}
This duality is due to the fact, that the sum of any ideals is the smallest ideal containing these ideals and the intersection of the ideals is the largest ideal contained in each of these ideals.\, Cf. sum of ideals,\, quotient of ideals.
\begin{thebibliography}{9}
J. Pahikkala:\, ``Some formulae for multiplying and inverting ideals''. $-$ \emph{Annales universitatis turkuensis} 183.\, Turun yliopisto (University of Turku) 1982.
\end{thebibliography}