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     2 <html>
       
     3 
       
     4 <!-- $Id$ -->
       
     5 
       
     6 <head>
       
     7 <title>The Isabelle Logo</title>
       
     8 </head>
       
     9 
       
    10 <body>
       
    11 
       
    12 <h1>The Isabelle Logo</h1>
       
    13 
       
    14 <h2>Versions</h2>
       
    15 
       
    16 The logo is available for the generic Isabelle system (<a
       
    17 href="#plain">plain</a>, <a href="#transparent">transparent</a>) and
       
    18 major object logics (<a href="#ZF">ZF</a>, <a href="#HOL">HOL</a>, <a
       
    19 href="#HOLCF">HOLCF</a>).
       
    20 
       
    21 
       
    22 <h2>Interpretation</h2>
       
    23 
       
    24 <img src="isabelle.gif" align=right alt="Isabelle logo"> First of all
       
    25 the logo tells about the name of the generic system, Isabelle, or of
       
    26 its concrete instantiations, e.g. Isabelle/HOL.  It also expresses
       
    27 some essentials of the overall Isabelle design philosophy: Composition
       
    28 of several small well understood building blocks, grouped together or
       
    29 arranged in layers. <p>
       
    30 
       
    31 The markings on the cubes illustrate this general principle by example
       
    32 of the core meta-logic (which is naively polymorphic simply typed
       
    33 lambda calculus with minimal higher-order logic). Thus red cubes
       
    34 symbolize the type system with function spaces (->) and type variables
       
    35 (alpha); violet ones represent the lambda term language with beta
       
    36 conversion etc.; yellow cubes constitute the actual logical parts,
       
    37 namely meta-implication or entailment (|-) and meta-level universal
       
    38 quantification.
       
    39 
       
    40 
       
    41 <h2>Acknowledgment</h2>
       
    42 
       
    43 The logo is contributed by Franziska Wenzel, Munich.  Thanks
       
    44 Franziska! <p>
       
    45 
       
    46 
       
    47 <p><hr><p>
       
    48 
       
    49 <a name="plain"><img src="isabelle.gif" alt="Isabelle logo"></a> <p>
       
    50 
       
    51 <a name="transparent"><img src="isabelle_transparent.gif"
       
    52 alt="Isabelle logo (transparent)"></a> <p>
       
    53 
       
    54 <a name="ZF"><img src="isabelle_zf.gif" alt="Isabelle logo (ZF)"></a>
       
    55 <p>
       
    56 
       
    57 <a name="HOL"><img src="isabelle_hol.gif" alt="Isabelle logo
       
    58 (HOL)"></a> <p>
       
    59 
       
    60 <a name="HOLCF"><img src="isabelle_holcf.gif" alt="Isabelle logo
       
    61 (HOLCF)"></a> <p>
       
    62 
       
    63 </body>
       
    64 </html>