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6 <meta content="text/html; charset=UTF-8" http-equiv="content-type"><title>λδ home page</title>
8 <meta content="Ferruccio Guidi" name="author">
9 <meta content="The formal system λδ" name="description">
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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>
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">
20 <td style="vertical-align: top;">
22 <li><a href="index.html">Foreword</a></li>
28 <li><a href="documentation.html">Papers</a></li>
31 <li><a href="implementation.html">Resources</a><br>
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>
39 <li><span style="font-weight: bold;">December 2012.</span> The character "_" is removed from the denomination "lambda_delta". <br>
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>
49 <li><span style="font-weight: bold;">September 2011.</span> The
50 denomination "lambda-delta" changes to "lambda_delta".
52 <li>The character "-" is reserved in λδ textual syntax
53 (recognized by <span style="font-style: italic;">Helena 0.8.1</span>).
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
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>.
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>
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>
85 <li><span style="font-weight: bold;">November 2010.</span> <span style="font-style: italic;">Helena 0.8.1</span> is released. <br>
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>
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>
98 <span style="font-weight: bold;"></span>
100 <li><span style="font-weight: bold;">September 2008.</span>
101 This site is online.<br>
104 <span style="font-weight: bold;"></span>
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>
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>
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>
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>
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>
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>
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>);
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>); <br>
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>
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>:
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>
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>
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>
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>
190 <li>we removed level indicators on environments (<span
191 style="font-style: italic;">cbk</span>).</li>
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>
200 <li><span style="font-weight: bold;">November 2006.</span> <a href="documentation.html#ldp3">λδ version 1</a> is released.</li>
203 <li><span style="font-weight: bold;">December 2005.</span> <a href="documentation.html#ldt1">First communication on λδ</a>.<br>
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>
211 <h3 style="text-align: right;">Visibility <img style="width: 37px; height: 37px;" alt="[Butterfly]" title="Butterfly" src="images/b4.png"></h3>
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>
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>
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230 Last update 2013-10-27 by <a href="http://www.cs.unibo.it/%7Efguidi/">Ferruccio