\newcommand\etalchar[1]$^#1$
<H2>Literatur</H2><UL>

<P><LI><TT>[Bor99]</TT>
Bernd Borchert.
<BR> Two dimensional languages.
<BR> <A HREF="http://math.uni-heidelberg.de/logic/bb/2dpapers.html"><TT>http://math.uni-heidelberg.de/logic/bb/2dpapers.html</TT></A>, 1999.

<P><LI><TT>[CDG\etalchar+97]</TT>
Hubert Comon, Max Dauchet, R\'emi Gilleron, Denis Lugiez, Sophie Tison, and
  Marc Tommasi.
<BR>  Tree Automata Techniques and Applications.
<BR> <A HREF="http://www.grappa.univ-lille3.fr/tata/"><TT>http://www.grappa.univ-lille3.fr/tata/</TT></A>, 1997.

<P><LI><TT>[EF99]</TT>
Heinz-Dieter Ebbinghaus and J\"org Flum.
<BR>  Finite Model Theory.
<BR> Springer, 1999.

<P><LI><TT>[EH99]</TT>
Joost Engelfriet and Hendrik~Jan Hoogeboom.
<BR>  Tree-Walking Pebble Automata, pages 72--83.
<BR> 1999.
<BR> <A HREF="http://www.wi.leidenuniv.nl/home/engelfri/pebble.ps.gz"><TT>http://www.wi.leidenuniv.nl/home/engelfri/pebble.ps.gz</TT></A>.

<P><LI><TT>[Eng99]</TT>
Joost Engelfriet.
<BR> Derivation trees of ground term rewriting systems.
<BR>  Information and Computation, 152(1):1--15, 1999.
<BR> technical report version
  <A HREF="http://www.wi.leidenuniv.nl/TechRep/1996/tr96-25.html"><TT>http://www.wi.leidenuniv.nl/TechRep/1996/tr96-25.html</TT></A>.

<P><LI><TT>[GR97]</TT>
Dora Giammarresi and Antonio Restivo.
<BR>  Two-Dimensional Languages, pages 215--267.
<BR> Volume~3 of Rozenberg and Salomaa \citeHFL, 1997.

<P><LI><TT>[GS97]</TT>
Ferenc G\'ecseg and Magnus Steinby.
<BR>  Tree Languages, pages 1--68.
<BR> Volume~3 of Rozenberg and Salomaa \citeHFL, 1997.

<P><LI><TT>[KM01]</TT>
Jarkko Kari and Cristopher Moore.
<BR> New results on alternating and non-deterministic two-dimensional
  finite-state automata.
<BR> In  Symposium on Theoretical Aspects of Computer Science
  (STACS), page~??, 2001.
<BR> <A HREF="http://www.santafe.edu/~moore/pubs/afa.html"><TT>http://www.santafe.edu/~moore/pubs/afa.html</TT></A>.

<P><LI><TT>[NS00]</TT>
Frank Neven and Thomas Schwentick.
<BR> On the power of tree-walking automata.
<BR> In  Automata, Languages and Programming, pages 547--560, 2000.
<BR> <A HREF="ftp://ftp.minet.uni-jena.de/pub/schwentick/NS00a.ps"><TT>ftp://ftp.minet.uni-jena.de/pub/schwentick/NS00a.ps</TT></A>.

<P><LI><TT>[Rei01]</TT>
Klaus Reinhardt.
<BR> The $\#a=\#b$ pictures are recognizable.
<BR> In  Proceedings of the 18th STACS, Dresden, pages 527--538,
  2001.
<BR> <A HREF="http://www-fs.informatik.uni-tuebingen.de/~reinhard/publ.html"><TT>http://www-fs.informatik.uni-tuebingen.de/~reinhard/publ.html</TT></A>.

<P><LI><TT>[RS97]</TT>
G.~Rozenberg and A.~Salomaa, editors.
<BR>  Handbook of Formal Languages.
<BR> Springer, 1997.

<P><LI><TT>[Sip89]</TT>
Michael Sipser.
<BR> Halting space-bounded computations.
<BR>  Theoretical Computer Science, pages 335--338, 1989.

<P><LI><TT>[Tho90]</TT>
Wolfgang Thomas.
<BR>  Automata on Infinite Objects, pages 133--192.
<BR> Volume~B of van Leeuwen \citeHTCS, 1990.

<P><LI><TT>[Tho97]</TT>
Wolfgang Thomas.
<BR>  Languages, Automata and Logic, pages 389--456.
<BR> Volume~3 of Rozenberg and Salomaa \citeHFL, 1997.

<P><LI><TT>[vL90]</TT>
Jan van Leeuwen, editor.
<BR>  Handbook of Theoretical Computer Science.
<BR> Elsevier Science Publishers B.V., 1990.

<P><LI><TT>[Wal01]</TT>
Johannes Waldmann.
<BR> Automaten, die auf b\"aumen spazierengehen.
<BR> Vortrag, Institut f. Informatik, Leipzig, 2001.
<BR> <A HREF="http://www.informatik.uni-leipzig.de/~joe/talk/twa.ps"><TT>http://www.informatik.uni-leipzig.de/~joe/talk/twa.ps</TT></A>.

</UL>