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\begin{document}
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\pagestyle{headings}
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\pagenumbering{arabic}
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\title{The Hahn-Banach Theorem \\ for Real Vector Spaces}
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\author{Gertrud Bauer \\ \url{http://www.in.tum.de/~bauerg/}}
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\maketitle
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\begin{abstract}
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  The Hahn-Banach Theorem is one of the most fundamental results in functional
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  analysis. We present a fully formal proof of two versions of the theorem,
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  one for general linear spaces and another for normed spaces.  This
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  development is based on simply-typed classical set-theory, as provided by
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  Isabelle/HOL.
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\end{abstract}
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\tableofcontents
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\parindent 0pt \parskip 0.5ex
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\clearpage
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\section{Preface}
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This is a fully formal proof of the Hahn-Banach Theorem. It closely follows
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the informal presentation given in Heuser's textbook \cite[{\S} 36]{Heuser:1986}.
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Another formal proof of the same theorem has been done in Mizar
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\cite{Nowak:1993}.  A general overview of the relevance and history of the
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Hahn-Banach Theorem is given by Narici and Beckenstein \cite{Narici:1996}.
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\medskip The document is structured as follows.  The first part contains
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definitions of basic notions of linear algebra: vector spaces, subspaces,
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normed spaces, continuous linear-forms, norm of functions and an order on
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functions by domain extension.  The second part contains some lemmas about the
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supremum (w.r.t.\ the function order) and extension of non-maximal functions.
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With these preliminaries, the main proof of the theorem (in its two versions)
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is conducted in the third part.  The dependencies of individual theories are
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as follows.
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\begin{center}
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  \includegraphics[scale=0.5]{session_graph}  
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\end{center}
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\clearpage
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\part {Basic Notions}
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\input{Bounds}
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\input{VectorSpace}
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\input{Subspace}
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\input{NormedSpace}
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\input{Linearform}
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\input{FunctionOrder}
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\input{FunctionNorm}
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\input{ZornLemma}
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\clearpage
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\part {Lemmas for the Proof}
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\input{HahnBanachSupLemmas}
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\input{HahnBanachExtLemmas}
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\input{HahnBanachLemmas}
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\clearpage
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\part {The Main Proof}
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\input{HahnBanach}
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\bibliographystyle{abbrv}
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\bibliography{root}
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\end{document}
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