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\begin{document}

\title{Quotients Revisited for Isabelle/HOL}

\author{Cezary Kaliszyk$^*$ and Christian Urban$^*$}

\institute{$^*$ Technical University of Munich, Germany}

\maketitle

\begin{abstract}

Higher-Order Logic (HOL) is based on a small logic kernel, whose only

mechanism for extension is the introduction of safe definitions and of

non-empty types. Both extensions are often performed in quotient

constructions. To ease the work involved with such quotient constructions, we

re-implemented in Isabelle/HOL the quotient package by Homeier. In doing so we

extended his work in order to deal with compositions of quotients. Also, we

designed our quotient package so that every step in a quotient construction

the procedure of lifting theorems from the raw level to the quotient level.

The importance for programming language research is that many properties of

programming language calculi are easier to verify over $\alpha$-equated, or

$\alpha$-quotient, terms, than over ``raw'' terms.

\end{abstract}

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\end{document}

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