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5   <title>lambda_delta home page</title>
6   <meta content="Ferruccio Guidi" name="author">
7   <meta content="The formal system lambda_delta" name="description">
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12 <br>
13 <a href="http://lambda-delta.info"><img alt="[Crux Logo]"
14  title="The Crux" src="download/crux_32.png"
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16 <h1>The Formal System λδ (lambda_delta)<br>
17 </h1>
18 <h2>Towards the unification of terms, types, environments and contexts</h2>
19 <img style="width: 95%; height: 4px;" alt="[Separator]"
20  title="Separator" src="download/rainbow.png"><br>
21 <table
22  style="text-align: left; width: 95%; margin-left: auto; margin-right: auto;"
23  border="0" cellpadding="2" cellspacing="20">
24   <tbody>
25     <tr>
26       <td style="vertical-align: top;">
27       <ul>
28         <li><a href="index.html">Foreword</a></li>
29       </ul>
30       <ul>
31         <li>News</li>
32       </ul>
33       <ul>
34         <li><a href="documentation.html">Papers</a></li>
35       </ul>
36       <ul>
37         <li><a href="implementation.html">Resources</a><br>
38         </li>
39       </ul>
40       </td>
41       <td style="vertical-align: top; text-align: left;">
42       <h3 style="text-align: right;">News <img
43  style="width: 37px; height: 37px;" alt="[Butterfly]" title="Butterfly"
44  src="download/b5.png"></h3>
45       <ul>
46         <li><span style="font-weight: bold;">September 2011.</span> The
47 denomination "lambda-delta" changes to "lambda_delta".</li>
48         <ul>
49           <li>The character "-" is reserved in λδ textual syntax
50 (recognized by <span style="font-style: italic;">Helena 0.8.1</span>).<br>
51           </li>
52           <li>Eventually, the occurrences of the character "-" will be
53 replaced by "_" in all λδ-related identifiers.</li>
54           <li>In particular, this refactoring involves file names and
55 path names.</li>
56           <li>The permanent λδ URL is sheduled to become <span
57  style="font-style: italic;">http://lambda_delta.info</span> on
58 December 2012.<br>
59           </li>
60         </ul>
61       </ul>
62       <ul>
63         <li><span style="font-weight: bold;">April 2011.</span> The
64 specification of λδ version 2 is restarted in <a
65  href="http://matita.cs.unibo.it/">Matita 0.5</a>.</li>
66         <ul>
67           <li><a href="ld_basic_2.html">Here</a> is a page about the
68 specification.<br>
69           </li>
70         </ul>
71       </ul>
72       <ul>
73         <li><span style="font-weight: bold;">December 2010.</span>
74 Permanent λδ URL acquired: <a href="http://lambda-delta.info">http://lambda-delta.info</a>
75 (pointing at this site). <br>
76           <span style="font-weight: bold;"></span></li>
77       </ul>
78       <ul>
79         <li><span style="font-weight: bold;">November 2010.</span> <span
80  style="font-style: italic;">Helena 0.8.1</span> is released. <br>
81         </li>
82       </ul>
83       <ul>
84         <li><span style="font-weight: bold;">September 2009.</span> <span
85  style="font-style: italic;">Helena 0.8.0</span> is released and the <a
86  href="implementation.html#lddl">λδ Digital Library</a> is
87 started.<br>
88           <span style="font-weight: bold;"></span></li>
89       </ul>
90       <ul>
91         <li><span style="font-weight: bold;">June 2009.</span> <span
92  style="font-style: italic;">Helena</span>, a <a
93  href="implementation.html#helena">validator for </a><a
94  href="implementation.html#helena">λ</a><a
95  href="implementation.html#helena">δ version 2</a><span
96  style="font-style: italic;"></span>, <span style="font-style: italic;"></span>is
97 available
98 as
99 a
100 part
101 of
102 the
103
104           <a href="http://helm.cs.unibo.it/">HELM</a> software. <br>
105         </li>
106       </ul>
107       <span style="font-weight: bold;"></span>
108       <ul>
109         <li><span style="font-weight: bold;">September 2008.</span>
110 This site is online.<br>
111         </li>
112       </ul>
113       <span style="font-weight: bold;"></span>
114       <ul>
115         <li><span style="font-weight: bold;">July 2008.</span> <a
116  href="documentation.html#tocl1">First journal paper on λδ</a> accepted
117 for publication.</li>
118       </ul>
119       <ul>
120         <li><span style="font-weight: bold;">July 2008.</span> First <a
121  href="http://helm.cs.unibo.it/procedural/">procedural
122 reconstruction</a> for <a href="http://matita.cs.unibo.it/">Matita 0.5</a>
123 of the <a href="implementation.html#source">λδ proof scripts for
124 Coq 7.3.1</a>.<br>
125         </li>
126       </ul>
127       <ul>
128         <li><span style="font-weight: bold;">June 2008.</span> The <a
129  href="implementation.html#static">HTML
130 pages of the specification of λδ version 1 for Matita 0.5</a> are
131 online.<br>
132           <span style="font-weight: bold;"></span></li>
133       </ul>
134       <ul>
135         <li><span style="font-weight: bold;">March 2008.</span> The
136 specification of λδ version 2 is started with Coq 7.3.1 (false start).
137 <!--          <ul>
138             <li>native type assignment with new rules for application: <span
139  style="font-style: italic;">nty</span> (it replaces <span
140  style="font-style: italic;">ty3</span>);<br>
141             </li>
142             <li>parallel conversion on focalized terms: <span
143  style="font-style: italic;">fpcs</span> (it replaces <span
144  style="font-style: italic;"></span><span style="font-style: italic;">pc3</span>);
145               <br>
146             </li>
147             <li>new weak parallel reduction on environments: <span
148  style="font-style: italic;">wcpr</span> <span
149  style="font-style: italic;"></span>(it is based on <span
150  style="font-style: italic;">fpr</span> and replaces <span
151  style="font-style: italic;">wcpr0</span>);&nbsp; <br>
152             </li>
153             <li>parallel reduction on focalized terms: <span
154  style="font-style: italic;">fpr</span> and <span
155  style="font-style: italic;">fprs</span> (they replace <span
156  style="font-style: italic;"></span><span style="font-style: italic;"></span><span
157  style="font-style: italic;">pr2</span>, <span
158  style="font-style: italic;">pr3</span>); <br>
159             </li>
160           </ul>
161           <ul>
162             <li>new thinning relation: <span
163  style="font-style: italic;">drop</span>
164 (it replaces the old <span style="font-style: italic;">drop</span>, <span
165  style="font-style: italic;">clear</span>, <span
166  style="font-style: italic;">getl</span>, <span
167  style="font-style: italic;">cimp</span>, <span
168  style="font-style: italic;">drop1</span>);</li>
169             <li>new shift function: <span style="font-style: italic;">shift</span>:
170 (it
171 replaces
172
173               <span style="font-style: italic;">app1</span>);</li>
174             <li>new length function for environments: <span
175  style="font-style: italic;">clen</span>;<br>
176             </li>
177             <li>new relocation function: <span
178  style="font-style: italic;">lift</span> (it replaces old <span
179  style="font-style: italic;">lift</span>, <span
180  style="font-style: italic;">lift1</span>);<br>
181             </li>
182             <li>new term structure with polarity indicators and no
183 distinction between binding and flat items;</li>
184             <li>new general theory of relocation (comprises new
185 relocation functions: <span style="font-style: italic;">s</span>, <span
186  style="font-style: italic;">r</span>);</li>
187             <li>we removed context-free reduction and conversion (<span
188  style="font-style: italic;">pr0</span>, <span
189  style="font-style: italic;">pr1</span>, <span
190  style="font-style: italic;">pc1</span>);<br>
191             </li>
192             <li>we removed greedy substitution (<span
193  style="font-style: italic;"></span><span style="font-style: italic;">csubst0</span>,
194               <span style="font-style: italic;">csubst1</span>, <span
195  style="font-style: italic;">fsubst0</span>, <span
196  style="font-style: italic;">subst0</span>, <span
197  style="font-style: italic;">subst1</span>);<br>
198             </li>
199             <li>we removed level indicators on environments (<span
200  style="font-style: italic;">cbk</span>).</li>
201           </ul>
202 --> </li>
203       </ul>
204       <ul>
205         <li><span style="font-weight: bold;">September 2007.</span>
206 The <a href="implementation.html#dynamic">specification of λδ version
207 1 for
208 Matita 0.4</a> is online.<br>
209         </li>
210       </ul>
211       <ul>
212         <li><span style="font-weight: bold;">December 2005.</span> <a
213  href="documentation.html#bologna1">First communication on λδ</a>.<br>
214         </li>
215       </ul>
216       <ul>
217         <li><span style="font-weight: bold;">May 2004.</span> The <a
218  href="implementation.html#source">specification of λδ version 1</a> is
219 started with Coq 7.3.1.<br>
220         </li>
221       </ul>
222       <h3 style="text-align: right;">Visibility <img
223  style="width: 37px; height: 37px;" alt="[Butterfly]" title="Butterfly"
224  src="download/b4.png"></h3>
225       <ul>
226         <li><span style="font-weight: bold;">February 2012.</span>
227 The <a href="http://www.google.com/">Google</a>
228 search for <span style="color: rgb(255, 0, 0);">formal system lambda
229 delta</span>
230 gives 5 resources about λδ in the first 6 results.<br>
231         </li>
232       </ul>
233       <ul>
234         <li><span style="font-weight: bold;">February 2012.</span>
235 The <a href="http://www.yahoo.com/">Yahoo</a>
236 search <span style="color: rgb(255, 0, 0);">formal system lambda delta</span>
237 gives this site as the first result.</li>
238       </ul>
239       </td>
240     </tr>
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256 Last update 2012-02-21 by <a href="http://www.cs.unibo.it/%7Efguidi/">Ferruccio
257 Guidi</a><br>
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