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6   <meta content="text/html; charset=UTF-8" http-equiv="content-type"><title>λδ home page</title>
7   
8   <meta content="Ferruccio Guidi" name="author">
9   <meta content="The formal system λδ" name="description">
10   <link rel="shortcut icon" href="images/crux_16.ico"></head><body>
11 <div style="text-align: center;"> <br>
12 <a href="http://lambdadelta.info/"><img alt="[Crux Logo]" title="The Crux" src="images/crux_32.png" style="border: 0px solid ; width: 32px; height: 32px;"></a>
13 <h1>The Formal System λδ (\lambda\delta)<br>
14 </h1>
15 <h2>Towards the unification of terms, types, environments and contexts</h2>
16 <img style="width: 95%; height: 4px;" alt="[Separator]" title="Separator" src="images/rainbow.png"><br>
17 <table style="text-align: left; width: 95%; margin-left: auto; margin-right: auto;" border="0" cellpadding="2" cellspacing="20">
18   <tbody>
19     <tr>
20       <td style="vertical-align: top;">
21       <ul>
22         <li><a href="index.html">Foreword</a></li>
23       </ul>
24       <ul>
25         <li>News</li>
26       </ul>
27       <ul>
28         <li><a href="documentation.html">Papers</a></li>
29       </ul>
30       <ul>
31         <li><a href="implementation.html">Resources</a><br>
32         </li>
33       </ul>
34       </td>
35       <td style="vertical-align: top; text-align: left;">
36       <h3 style="text-align: right;">News <img style="width: 37px; height: 37px;" alt="[Butterfly]" title="Butterfly" src="images/b5.png"></h3>
37       <ul>
38         
39         <li><span style="font-weight: bold;">December 2012.</span> The character "_" is removed from the denomination "lambda_delta". <br>
40         </li>
41         <ul>
42           <li>The denomination "\lambda\delta" is used in λδ-related texts.</li>
43           <li>The denomination "lambdadelta" is used in λδ-related identifiers.</li>
44           <li>Permanent λδ URL acquired: <a href="http://lambdadelta.info/">http://lambdadelta.info/</a>
45 (pointing at this site). </li>
46         </ul>
47 </ul>
48       <ul>
49         <li><span style="font-weight: bold;">September 2011.</span> The
50 denomination "lambda-delta" changes to "lambda_delta".
51           <ul>
52             <li>The character "-" is reserved in λδ textual syntax
53 (recognized by <span style="font-style: italic;">Helena 0.8.1</span>).
54             </li>
55             <li>Eventually, the occurrences of the character "-" will
56 be replaced by "_" in all λδ-related identifiers.</li>
57             <li>In particular, this refactoring involves file names and
58 path names.</li>
59             
60           </ul>
61         </li>
62
63       
64       </ul>
65
66       <ul>
67         <li><span style="font-weight: bold;">April 2011.</span> The
68 specification of λδ version 2 and related topics is restarted in <a href="http://matita.cs.unibo.it/">Matita 0.5</a>.
69           <ul>
70             <li><a href="apps_2.html">Here</a> is a page about the
71 topics related to the specification (Applications).</li>
72             <li><a href="basic_2.html">Here</a> is a page about the
73 specification (Core). </li>
74             <li><a href="ground_2.html">Here</a> is a page about the
75 background of the specification (Ground).</li>
76           </ul>
77         </li>
78       </ul>
79       <ul>
80         <li><span style="font-weight: bold;">December 2010.</span> Transient λδ URL acquired: http://lambda-delta.info/
81 (expires on December 2012). <br>
82           <span style="font-weight: bold;"></span></li>
83       </ul>
84       <ul>
85         <li><span style="font-weight: bold;">November 2010.</span> <span style="font-style: italic;">Helena 0.8.1</span> is released. <br>
86         </li>
87       </ul>
88       <ul>
89         <li><span style="font-weight: bold;">September 2009.</span> <span style="font-style: italic;">Helena 0.8.0</span> is released and the <a href="implementation.html#lddl">λδ Digital Library</a> is started.<br>
90           <span style="font-weight: bold;"></span></li>
91       </ul>
92       <ul>
93         <li><span style="font-weight: bold;">June 2009.</span> <span style="font-style: italic;">Helena</span>, a <a href="implementation.html#helena">validator for λδ version 2</a>, is
94 available as a part of the <a href="http://helm.cs.unibo.it/">HELM</a>
95 software. <br>
96         </li>
97       </ul>
98       <span style="font-weight: bold;"></span>
99       <ul>
100         <li><span style="font-weight: bold;">September 2008.</span>
101 This site is online.<br>
102         </li>
103       </ul>
104       <span style="font-weight: bold;"></span>
105       <ul>
106         <li><span style="font-weight: bold;">July 2008.</span> <a href="documentation.html#ldp5">First journal paper on λδ</a> accepted
107 for publication.</li>
108       </ul>
109       <ul>
110         <li><span style="font-weight: bold;">July 2008.</span> First <a href="http://helm.cs.unibo.it/procedural/">procedural reconstruction</a>
111 for <a href="http://matita.cs.unibo.it/">Matita 0.5</a> of the <a href="implementation.html#ldp1">λδ proof scripts for Coq 7.3.1</a>.<br>
112         </li>
113       </ul>
114       <ul>
115         <li><span style="font-weight: bold;">June 2008.</span> The <a href="implementation.html#static">HTML pages of the specification of
116 λδ version 1 for Matita 0.5</a> are online.<br>
117           <span style="font-weight: bold;"></span></li>
118       </ul>
119       <ul>
120         <li><span style="font-weight: bold;">May 2008.</span> The
121 specification of λδ version 1 is dismissed.<br>
122           <span style="font-weight: bold;"></span></li>
123       </ul>
124       <ul>
125         <li><span style="font-weight: bold;">March 2008.</span> The
126 specification of λδ version 2 is started with Coq 7.3.1 (false start). </li>
127       </ul>
128 <!--          <ul>
129             <li>native type assignment with new rules for application: <span
130  style="font-style: italic;">nty</span> (it replaces <span
131  style="font-style: italic;">ty3</span>);<br>
132             </li>
133             <li>parallel conversion on focalized terms: <span
134  style="font-style: italic;">fpcs</span> (it replaces <span
135  style="font-style: italic;"></span><span style="font-style: italic;">pc3</span>);
136               <br>
137             </li>
138             <li>new weak parallel reduction on environments: <span
139  style="font-style: italic;">wcpr</span> <span
140  style="font-style: italic;"></span>(it is based on <span
141  style="font-style: italic;">fpr</span> and replaces <span
142  style="font-style: italic;">wcpr0</span>);&nbsp; <br>
143             </li>
144             <li>parallel reduction on focalized terms: <span
145  style="font-style: italic;">fpr</span> and <span
146  style="font-style: italic;">fprs</span> (they replace <span
147  style="font-style: italic;"></span><span style="font-style: italic;"></span><span
148  style="font-style: italic;">pr2</span>, <span
149  style="font-style: italic;">pr3</span>); <br>
150             </li>
151           </ul>
152           <ul>
153             <li>new thinning relation: <span
154  style="font-style: italic;">drop</span>
155 (it replaces the old <span style="font-style: italic;">drop</span>, <span
156  style="font-style: italic;">clear</span>, <span
157  style="font-style: italic;">getl</span>, <span
158  style="font-style: italic;">cimp</span>, <span
159  style="font-style: italic;">drop1</span>);</li>
160             <li>new shift function: <span style="font-style: italic;">shift</span>:
161 (it
162 replaces
163
164               <span style="font-style: italic;">app1</span>);</li>
165             <li>new length function for environments: <span
166  style="font-style: italic;">clen</span>;<br>
167             </li>
168             <li>new relocation function: <span
169  style="font-style: italic;">lift</span> (it replaces old <span
170  style="font-style: italic;">lift</span>, <span
171  style="font-style: italic;">lift1</span>);<br>
172             </li>
173             <li>new term structure with polarity indicators and no
174 distinction between binding and flat items;</li>
175             <li>new general theory of relocation (comprises new
176 relocation functions: <span style="font-style: italic;">s</span>, <span
177  style="font-style: italic;">r</span>);</li>
178             <li>we removed context-free reduction and conversion (<span
179  style="font-style: italic;">pr0</span>, <span
180  style="font-style: italic;">pr1</span>, <span
181  style="font-style: italic;">pc1</span>);<br>
182             </li>
183             <li>we removed greedy substitution (<span
184  style="font-style: italic;"></span><span style="font-style: italic;">csubst0</span>,
185               <span style="font-style: italic;">csubst1</span>, <span
186  style="font-style: italic;">fsubst0</span>, <span
187  style="font-style: italic;">subst0</span>, <span
188  style="font-style: italic;">subst1</span>);<br>
189             </li>
190             <li>we removed level indicators on environments (<span
191  style="font-style: italic;">cbk</span>).</li>
192           </ul>
193 -->
194       <ul>
195         <li><span style="font-weight: bold;">September 2007.</span> The
196           <a href="implementation.html#dynamic">specification of λδ
197 version 1 for Matita 0.4</a> is online.</li>
198       </ul>
199       <ul>
200         <li><span style="font-weight: bold;">November 2006.</span> <a href="documentation.html#ldp3">λδ version 1</a> is released.</li>
201       </ul>
202       <ul>
203         <li><span style="font-weight: bold;">December 2005.</span> <a href="documentation.html#ldt1">First communication on λδ</a>.<br>
204         </li>
205       </ul>
206       <ul>
207         <li><span style="font-weight: bold;">May 2004.</span> The <a href="implementation.html#ldp1">specification of λδ version 1</a> is
208 started with Coq 7.3.1.<br>
209         </li>
210       </ul>
211       <h3 style="text-align: right;">Visibility <img style="width: 37px; height: 37px;" alt="[Butterfly]" title="Butterfly" src="images/b4.png"></h3>
212       <ul>
213         <li><span style="font-weight: bold;">February 2012.</span> The <a href="http://www.google.com/">Google</a> search for <span style="color: rgb(255, 0, 0);">formal system lambda delta</span> gives
214 5 resources about λδ in the first 6 results.<br>
215         </li>
216       </ul>
217       <ul>
218         <li><span style="font-weight: bold;">February 2012.</span> The <a href="http://www.yahoo.com/">Yahoo</a> search <span style="color: rgb(255, 0, 0);">formal system lambda delta</span> gives
219 this site as the first result.</li>
220       </ul>
221       </td>
222     </tr>
223   </tbody>
224 </table>
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230 Last update 2013-10-27 by <a href="http://www.cs.unibo.it/%7Efguidi/">Ferruccio
231
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