Add documentation for temporal logic operators.

* doc/tl/Makefile.am, doc/tl/tl.tex, doc/tl/tl.bib: New files.
* doc/Makefile.am (SUBDIRS): Recurse into tl/.
* configure.ac: Output doc/tl/Makefile
* README: Describe doc/tl/.

doc/tl/tl.bib

@@ -0,0 +1,101 @@
+@InProceedings{	  somenzi.00.cav,
+  author	= {Fabio Somenzi and Roderick Bloem},
+  title		= {Efficient {B\"u}chi Automata for {LTL} Formul{\ae}},
+  booktitle	= {Proceedings of the 12th International Conference on
+		  Computer Aided Verification (CAV'00)},
+  pages		= {247--263},
+  year		= {2000},
+  volume	= {1855},
+  series	= {Lecture Notes in Computer Science},
+  address	= {Chicago, Illinois, USA},
+  publisher	= {Springer-Verlag}
+}
+
+@InProceedings{	  etessami.00.concur,
+  author	= {Kousha Etessami and Gerard J. Holzmann},
+  title		= {Optimizing {B\"u}chi Automata},
+  booktitle	= {Proceedings of the 11th International Conference on
+		  Concurrency Theory (Concur'00)},
+  pages		= {153--167},
+  year		= {2000},
+  editor	= {C. Palamidessi},
+  volume	= {1877},
+  series	= {Lecture Notes in Computer Science},
+  address	= {Pennsylvania, USA},
+  publisher	= {Springer-Verlag},
+  note          = {Beware of a typo in the version from the
+                  proceedings: $f \U g$ is purely eventual if both
+                  operands are purely eventual.  The revision of the
+                  paper available at
+                  \url{http://www.bell-labs.com/project/TMP/} is
+                  fixed.  We fixed the bug in Spot in 2005, thanks to
+                  LBTT.  See also \url{http://arxiv.org/abs/1011.4214v2}
+                  for a discussion about this problem.}
+}
+
+@InProceedings{manna.87.podc,
+ author = {Zohar Manna and Amir Pnueli},
+ title = {A hierarchy of temporal properties},
+ booktitle = {Proceedings of the sixth annual ACM Symposium on Principles of distributed computing (PODC'90)},
+ year = {1990},
+ location = {Quebec City, Canada},
+ pages = {377--410},
+ publisher = {ACM},
+ address = {New York, NY, USA},
+}
+
+@InProceedings{	  chang.92.icalp,
+  author	= {Edward Y. Chang and Zohar Manna and Amir Pnueli},
+  title		= {Characterization of Temporal Property Classes},
+  booktitle	= {Proceedings of the 19th International Colloquium on
+		  Automata, Languages and Programming (ICALP'92)},
+  year		= {1992},
+  pages		= {474--486},
+  publisher	= {Springer-Verlag},
+  address	= {London, UK}
+}
+
+@InProceedings{	  cerna.03.mfcs,
+  author	= {Ivana {\v{C}}ern{\'a} and Radek Pel{\'a}nek},
+  title		= {Relating Hierarchy of Temporal Properties to Model
+		  Checking},
+  booktitle	= {Proceedings of the 28th International Symposium on
+		  Mathematical Foundations of Computer Science (MFCS'03)},
+  pages		= {318--327},
+  year		= {2003},
+  editor	= {Branislav Rovan and Peter Vojt{\'a}{\v{a}}},
+  volume	= {2747},
+  series	= {Lecture Notes in Computer Science},
+  address	= {Bratislava, Slovak Republic},
+  month		= aug,
+  publisher	= {Springer-Verlag}
+}
+
+@InProceedings{	  schneider.01.lpar,
+  author	= {Klaus Schneider},
+  title		= {Improving Automata Generation for Linear Temporal Logic by
+		  Considering the Automaton Hierarchy},
+  booktitle	= {Proceedings of the 8th International Conference on Logic
+		  for Programming, Artificial Intelligence and Reasoning},
+  pages		= {39--54},
+  year		= {2001},
+  volume	= {2250},
+  series	= {Lecture Notes in Artificial Intelligence},
+  address	= {Havana, Cuba},
+  publisher	= {Springer-Verlag}
+}
+
+@TechReport{	  tauriainen.03.a83,
+  author	= {Heikki Tauriainen},
+  title		= {On Translating Linear Temporal Logic into Alternating and
+		  Nondeterministic Automata},
+  institution	= {Helsinki University of Technology, Laboratory for
+		  Theoretical Computer Science},
+  address	= {Espoo, Finland},
+  month		= dec,
+  number	= {A83},
+  pages		= {132},
+  type		= {Research Report},
+  year		= {2003},
+  note		= {Reprint of Licentiate's thesis}
+}