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5 <title>lambda_delta home page</title>
6 <meta content="Ferruccio Guidi" name="author">
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15 <h1>The Formal System λδ (lambda_delta)<br>
17 <h2>Towards the unification of terms, types, environments and contexts</h2>
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25 <td style="vertical-align: top;">
27 <li><a href="index.html">Foreword</a></li>
33 <li><a href="documentation.html">Papers</a></li>
36 <li><a href="implementation.html">Resources</a><br>
40 <td style="vertical-align: top; text-align: left;">
41 <h3 style="text-align: right;">News <img
42 style="width: 37px; height: 37px;" alt="[Butterfly]" title="Butterfly"
43 src="download/b5.png"></h3>
45 <li><span style="font-weight: bold;">September 2011.</span> The
46 denomination "lambda-delta" changes to "lambda_delta".
48 <li>The character "-" is reserved in λδ textual syntax
49 (recognized by <span style="font-style: italic;">Helena 0.8.1</span>).
51 <li>Eventually, the occurrences of the character "-" will
52 be replaced by "_" in all λδ-related identifiers.</li>
53 <li>In particular, this refactoring involves file names and
55 <li>The permanent λδ URL is sheduled to become <span
56 style="font-style: italic;">http://lambda_delta.info</span> on
63 <li><span style="font-weight: bold;">April 2011.</span> The
64 specification of λδ version 2 and related topics is restarted in <a
65 href="http://matita.cs.unibo.it/">Matita 0.5</a>.
67 <li><a href="apps_2.html">Here</a> is a page about the
68 topics related to the specification (Applications).</li>
69 <li><a href="basic_2.html">Here</a> is a page about the
70 specification (Core). </li>
75 <li><span style="font-weight: bold;">December 2010.</span>
76 Permanent λδ URL acquired: <a href="http://lambda-delta.info">http://lambda-delta.info</a>
77 (pointing at this site). <br>
78 <span style="font-weight: bold;"></span></li>
81 <li><span style="font-weight: bold;">November 2010.</span> <span
82 style="font-style: italic;">Helena 0.8.1</span> is released. <br>
86 <li><span style="font-weight: bold;">September 2009.</span> <span
87 style="font-style: italic;">Helena 0.8.0</span> is released and the <a
88 href="implementation.html#lddl">λδ Digital Library</a> is started.<br>
89 <span style="font-weight: bold;"></span></li>
92 <li><span style="font-weight: bold;">June 2009.</span> <span
93 style="font-style: italic;">Helena</span>, a <a
94 href="implementation.html#helena">validator for λδ version 2</a>, is
95 available as a part of the <a href="http://helm.cs.unibo.it/">HELM</a>
99 <span style="font-weight: bold;"></span>
101 <li><span style="font-weight: bold;">September 2008.</span>
102 This site is online.<br>
105 <span style="font-weight: bold;"></span>
107 <li><span style="font-weight: bold;">July 2008.</span> <a
108 href="documentation.html#ldp5">First journal paper on λδ</a> accepted
109 for publication.</li>
112 <li><span style="font-weight: bold;">July 2008.</span> First <a
113 href="http://helm.cs.unibo.it/procedural/">procedural reconstruction</a>
114 for <a href="http://matita.cs.unibo.it/">Matita 0.5</a> of the <a
115 href="implementation.html#ldp1">λδ proof scripts for Coq 7.3.1</a>.<br>
119 <li><span style="font-weight: bold;">June 2008.</span> The <a
120 href="implementation.html#static">HTML pages of the specification of
121 λδ version 1 for Matita 0.5</a> are online.<br>
122 <span style="font-weight: bold;"></span></li>
125 <li><span style="font-weight: bold;">May 2008.</span> The
126 specification of λδ version 1 is closed.<br>
127 <span style="font-weight: bold;"></span></li>
130 <li><span style="font-weight: bold;">March 2008.</span> The
131 specification of λδ version 2 is started with Coq 7.3.1 (false start). </li>
134 <li>native type assignment with new rules for application: <span
135 style="font-style: italic;">nty</span> (it replaces <span
136 style="font-style: italic;">ty3</span>);<br>
138 <li>parallel conversion on focalized terms: <span
139 style="font-style: italic;">fpcs</span> (it replaces <span
140 style="font-style: italic;"></span><span style="font-style: italic;">pc3</span>);
143 <li>new weak parallel reduction on environments: <span
144 style="font-style: italic;">wcpr</span> <span
145 style="font-style: italic;"></span>(it is based on <span
146 style="font-style: italic;">fpr</span> and replaces <span
147 style="font-style: italic;">wcpr0</span>); <br>
149 <li>parallel reduction on focalized terms: <span
150 style="font-style: italic;">fpr</span> and <span
151 style="font-style: italic;">fprs</span> (they replace <span
152 style="font-style: italic;"></span><span style="font-style: italic;"></span><span
153 style="font-style: italic;">pr2</span>, <span
154 style="font-style: italic;">pr3</span>); <br>
158 <li>new thinning relation: <span
159 style="font-style: italic;">drop</span>
160 (it replaces the old <span style="font-style: italic;">drop</span>, <span
161 style="font-style: italic;">clear</span>, <span
162 style="font-style: italic;">getl</span>, <span
163 style="font-style: italic;">cimp</span>, <span
164 style="font-style: italic;">drop1</span>);</li>
165 <li>new shift function: <span style="font-style: italic;">shift</span>:
169 <span style="font-style: italic;">app1</span>);</li>
170 <li>new length function for environments: <span
171 style="font-style: italic;">clen</span>;<br>
173 <li>new relocation function: <span
174 style="font-style: italic;">lift</span> (it replaces old <span
175 style="font-style: italic;">lift</span>, <span
176 style="font-style: italic;">lift1</span>);<br>
178 <li>new term structure with polarity indicators and no
179 distinction between binding and flat items;</li>
180 <li>new general theory of relocation (comprises new
181 relocation functions: <span style="font-style: italic;">s</span>, <span
182 style="font-style: italic;">r</span>);</li>
183 <li>we removed context-free reduction and conversion (<span
184 style="font-style: italic;">pr0</span>, <span
185 style="font-style: italic;">pr1</span>, <span
186 style="font-style: italic;">pc1</span>);<br>
188 <li>we removed greedy substitution (<span
189 style="font-style: italic;"></span><span style="font-style: italic;">csubst0</span>,
190 <span style="font-style: italic;">csubst1</span>, <span
191 style="font-style: italic;">fsubst0</span>, <span
192 style="font-style: italic;">subst0</span>, <span
193 style="font-style: italic;">subst1</span>);<br>
195 <li>we removed level indicators on environments (<span
196 style="font-style: italic;">cbk</span>).</li>
200 <li><span style="font-weight: bold;">September 2007.</span> The
201 <a href="implementation.html#dynamic">specification of λδ
202 version 1 for Matita 0.4</a> is online.</li>
205 <li><span style="font-weight: bold;">November 2006.</span> <a
206 href="documentation.html#ldp3">λδ version 1</a> is released.</li>
209 <li><span style="font-weight: bold;">December 2005.</span> <a
210 href="documentation.html#ldt1">First communication on λδ</a>.<br>
214 <li><span style="font-weight: bold;">May 2004.</span> The <a
215 href="implementation.html#ldp1">specification of λδ version 1</a> is
216 started with Coq 7.3.1.<br>
219 <h3 style="text-align: right;">Visibility <img
220 style="width: 37px; height: 37px;" alt="[Butterfly]" title="Butterfly"
221 src="download/b4.png"></h3>
223 <li><span style="font-weight: bold;">February 2012.</span> The <a
224 href="http://www.google.com/">Google</a> search for <span
225 style="color: rgb(255, 0, 0);">formal system lambda delta</span> gives
226 5 resources about λδ in the first 6 results.<br>
230 <li><span style="font-weight: bold;">February 2012.</span> The <a
231 href="http://www.yahoo.com/">Yahoo</a> search <span
232 style="color: rgb(255, 0, 0);">formal system lambda delta</span> gives
233 this site as the first result.</li>
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254 Last update 2012-11-20 by <a href="http://www.cs.unibo.it/%7Efguidi/">Ferruccio