| 9375 |      1 | \documentclass[10pt,a4paper,twoside]{article}
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| 11851 |      2 | \usepackage{graphicx}
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| 7917 |      3 | \usepackage{latexsym,theorem}
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| 10687 |      4 | \usepackage{isabelle,isabellesym}
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| 7984 |      5 | \usepackage{pdfsetup} %last one!
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| 10687 |      6 | 
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|  |      7 | \isabellestyle{it}
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| 9659 |      8 | \urlstyle{rm}
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| 7747 |      9 | 
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| 10687 |     10 | \newcommand{\isasymsup}{\isamath{\sup\,}}
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|  |     11 | \newcommand{\skp}{\smallskip}
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|  |     12 | 
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| 7808 |     13 | 
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| 7747 |     14 | \begin{document}
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|  |     15 | 
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| 7917 |     16 | \pagestyle{headings}
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|  |     17 | \pagenumbering{arabic}
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|  |     18 | 
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| 11851 |     19 | \title{The Hahn-Banach Theorem \\ for Real Vector Spaces}
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| 7978 |     20 | \author{Gertrud Bauer \\ \url{http://www.in.tum.de/~bauerg/}}
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|  |     21 | \maketitle
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| 7747 |     22 | 
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| 7808 |     23 | \begin{abstract}
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| 7978 |     24 |   The Hahn-Banach Theorem is one of the most fundamental results in functional
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| 7927 |     25 |   analysis. We present a fully formal proof of two versions of the theorem,
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|  |     26 |   one for general linear spaces and another for normed spaces.  This
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|  |     27 |   development is based on simply-typed classical set-theory, as provided by
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|  |     28 |   Isabelle/HOL.
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| 7808 |     29 | \end{abstract}
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|  |     30 | 
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| 7927 |     31 | 
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| 7808 |     32 | \tableofcontents
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| 7927 |     33 | \parindent 0pt \parskip 0.5ex
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|  |     34 | 
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|  |     35 | \clearpage
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|  |     36 | \section{Preface}
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| 7808 |     37 | 
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| 7978 |     38 | This is a fully formal proof of the Hahn-Banach Theorem. It closely follows
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| 15084 |     39 | the informal presentation given in Heuser's textbook \cite[{\S} 36]{Heuser:1986}.
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| 7927 |     40 | Another formal proof of the same theorem has been done in Mizar
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|  |     41 | \cite{Nowak:1993}.  A general overview of the relevance and history of the
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| 15084 |     42 | Hahn-Banach Theorem is given by Narici and Beckenstein \cite{Narici:1996}.
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| 7927 |     43 | 
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|  |     44 | \medskip The document is structured as follows.  The first part contains
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|  |     45 | definitions of basic notions of linear algebra: vector spaces, subspaces,
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| 11851 |     46 | normed spaces, continuous linear-forms, norm of functions and an order on
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| 7927 |     47 | functions by domain extension.  The second part contains some lemmas about the
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|  |     48 | supremum (w.r.t.\ the function order) and extension of non-maximal functions.
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|  |     49 | With these preliminaries, the main proof of the theorem (in its two versions)
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| 11851 |     50 | is conducted in the third part.  The dependencies of individual theories are
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|  |     51 | as follows.
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| 7927 |     52 | 
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| 11851 |     53 | \begin{center}
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| 13548 |     54 |   \includegraphics[scale=0.5]{session_graph}  
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| 11851 |     55 | \end{center}
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| 7927 |     56 | 
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|  |     57 | \clearpage
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|  |     58 | \part {Basic Notions}
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| 7917 |     59 | 
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| 10687 |     60 | \input{Bounds}
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|  |     61 | \input{VectorSpace}
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|  |     62 | \input{Subspace}
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|  |     63 | \input{NormedSpace}
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|  |     64 | \input{Linearform}
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|  |     65 | \input{FunctionOrder}
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|  |     66 | \input{FunctionNorm}
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|  |     67 | \input{ZornLemma}
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| 7917 |     68 | 
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| 7927 |     69 | \clearpage
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|  |     70 | \part {Lemmas for the Proof}
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| 7917 |     71 | 
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| 10687 |     72 | \input{HahnBanachSupLemmas}
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|  |     73 | \input{HahnBanachExtLemmas}
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|  |     74 | \input{HahnBanachLemmas}
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| 7917 |     75 | 
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| 7927 |     76 | \clearpage
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|  |     77 | \part {The Main Proof}
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| 7917 |     78 | 
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| 10687 |     79 | \input{HahnBanach}
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| 7917 |     80 | \bibliographystyle{abbrv}
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| 7927 |     81 | \bibliography{root}
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| 7747 |     82 | 
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|  |     83 | \end{document}
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