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16 <h1>The Formal System λδ (lambda-delta)<br>
18 <h2>Towards the unification of terms, types, environments and contexts</h2>
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26 <td style="vertical-align: top;">
28 <li><a href="index.html">Foreword</a></li>
34 <li><a href="documentation.html">Papers</a></li>
37 <li><a href="implementation.html">Resources</a><br>
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>
46 <li><span style="font-weight: bold;">December 2010.</span>
47 Permanent λδ URL acquired: <a href="http://lambda-delta.info">http://lambda-delta.info</a>
48 (pointing at this site). <br>
49 <span style="font-weight: bold;"></span></li>
52 <li><span style="font-weight: bold;">November 2010.</span> <span
53 style="font-style: italic;">Helena 0.8.1</span> is released. <br>
57 <li><span style="font-weight: bold;">September 2009.</span> <span
58 style="font-style: italic;">Helena 0.8.0</span> is released and the <a
59 href="implementation.html#lddl">λδ Digital Library</a> is
61 <span style="font-weight: bold;"></span></li>
64 <li><span style="font-weight: bold;">June 2009.</span> <span
65 style="font-style: italic;">Helena</span>, A <a
66 href="implementation.html#helena">validator for </a><a
67 href="implementation.html#helena">λδ</a><span
68 style="font-style: italic;"></span>, <span style="font-style: italic;"></span>is
71 part of the <a href="http://helm.cs.unibo.it/">HELM</a> software. <br>
74 <span style="font-weight: bold;"></span>
76 <li><span style="font-weight: bold;">September 2008.</span>
77 This site is online.<br>
80 <span style="font-weight: bold;"></span>
82 <li><span style="font-weight: bold;">July 2008.</span> <a
83 href="documentation.html#tocl1">First journal paper on λδ</a> accepted
87 <li><span style="font-weight: bold;">July 2008.</span> First <a
88 href="http://helm.cs.unibo.it/procedural/">procedural
89 reconstruction</a> in <a href="http://matita.cs.unibo.it/">Matita 0.5</a>
90 of the <a href="implementation.html#source">λδ proof scripts in
95 <li><span style="font-weight: bold;">June 2008.</span> The <a
96 href="implementation.html#static">HTML
97 pages of the specification of λδ in Matita 0.5</a> are online.<br>
98 <span style="font-weight: bold;"></span></li>
101 <li><span style="font-weight: bold;">March 2008.</span> An
103 specification of λδ in Coq 7.3.1 begins:
105 <li>native type assignment with new rules for application: <span
106 style="font-style: italic;">nty</span> (it replaces <span
107 style="font-style: italic;">ty3</span>);<br>
109 <li>parallel conversion on focalized terms: <span
110 style="font-style: italic;">fpcs</span> (it replaces <span
111 style="font-style: italic;"></span><span style="font-style: italic;">pc3</span>);
121 <li>new weak parallel reduction on environments: <span
122 style="font-style: italic;">wcpr</span> <span
123 style="font-style: italic;"></span>(it is based on <span
124 style="font-style: italic;">fpr</span> and replaces <span
125 style="font-style: italic;">wcpr0</span>); <br>
127 <li>parallel reduction on focalized terms: <span
128 style="font-style: italic;">fpr</span> and <span
129 style="font-style: italic;">fprs</span> (they replace <span
130 style="font-style: italic;"></span><span style="font-style: italic;"></span><span
131 style="font-style: italic;">pr2</span>, <span
132 style="font-style: italic;">pr3</span>); <br>
136 <li>new thinning relation: <span
137 style="font-style: italic;">drop</span>
138 (it replaces the old <span style="font-style: italic;">drop</span>, <span
139 style="font-style: italic;">clear</span>, <span
140 style="font-style: italic;">getl</span>, <span
141 style="font-style: italic;">cimp</span>, <span
142 style="font-style: italic;">drop1</span>);</li>
143 <li>new shift function: <span style="font-style: italic;">shift</span>:
146 <span style="font-style: italic;">app1</span>);</li>
147 <li>new length function for environments: <span
148 style="font-style: italic;">clen</span>;<br>
150 <li>new relocation function: <span
151 style="font-style: italic;">lift</span> (it replaces old <span
152 style="font-style: italic;">lift</span>, <span
153 style="font-style: italic;">lift1</span>);<br>
155 <li>new term structure with polarity indicators and no
156 distinction between binding and flat items;</li>
157 <li>new general theory of relocation (comprises new
158 relocation functions: <span style="font-style: italic;">s</span>, <span
159 style="font-style: italic;">r</span>);</li>
160 <li>we removed context-free reduction and conversion (<span
161 style="font-style: italic;">pr0</span>, <span
162 style="font-style: italic;">pr1</span>, <span
163 style="font-style: italic;">pc1</span>);<br>
165 <li>we removed greedy substitution (<span
166 style="font-style: italic;"></span><span style="font-style: italic;">csubst0</span>,
169 <span style="font-style: italic;">csubst1</span>, <span
170 style="font-style: italic;">fsubst0</span>, <span
171 style="font-style: italic;">subst0</span>, <span
172 style="font-style: italic;">subst1</span>);<br>
174 <li>we removed level indicators on environments (<span
175 style="font-style: italic;">cbk</span>).</li>
180 <li><span style="font-weight: bold;">September 2007.</span>
181 The <a href="implementation.html#dynamic">specification of λδ in
182 Matita 0.4</a> is online.<br>
186 <li><span style="font-weight: bold;">December 2005.</span> <a
187 href="documentation.html#bologna1">First communication on λδ</a>.<br>
191 <li><span style="font-weight: bold;">May 2004.</span> The <a
192 href="implementation.html#source">specification of λδ in
193 Coq 7.3.1</a> begins.<br>
196 <h3 style="text-align: right;">Visibility <img
197 style="width: 37px; height: 37px;" alt="[Butterfly]" title="Butterfly"
198 src="download/b4.png"></h3>
200 <li><span style="font-weight: bold;">November 2010.</span> The <a
201 href="http://www.google.com/">Google</a>
202 search <span style="color: rgb(255, 0, 0);">formal system lambda delta</span>
203 gives 8 resources about λδ as the first results.<br>
207 <li><span style="font-weight: bold;">November 2010.</span> The <a
208 href="http://www.yahoo.com/">Yahoo</a>
209 search <span style="color: rgb(255, 0, 0);">formal system lambda delta</span>
210 gives 4 resources and 2 sub-resources about λδ as the first results.</li>
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230 Last update 2010-12-14 by <a href="http://www.cs.unibo.it/%7Efguidi/">Ferruccio