<bibliography>
 <citation type="article" key="Cul78">
  <author>K. Culik, II</author>
  <year>1978</year>
  <title>The decidability of &#965;-local catenativity and of other properties of D0L systems</title>
  <journal>Information Processing Lett.</journal>
  <volume>7</volume>
  <number>1</number>
  <pages>33&#8211;35</pages>
  <doi>10.1016/0020-0190(78)90035-2</doi>
 </citation>
 <citation type="article" key="ER78">
  <author>A. Ehrenfeucht</author>
  <author>G. Rozenberg</author>
  <year>1978</year>
  <title>Simplifications of homomorphisms</title>
  <journal>Inform. and Control</journal>
  <volume>38</volume>
  <number>3</number>
  <pages>298&#8211;309</pages>
  <doi>10.1016/S0019-9958(78)90095-5</doi>
 </citation>
 <citation type="inproceedings" key="HHKR10">
  <author>V. Halava</author>
  <author>T. Harju</author>
  <author>T. K&#228;rki</author>
  <author>M. Rigo</author>
  <year>2010</year>
  <title>On the periodicity of morphic words</title>
  <editor>Y. Gao</editor>
  <editor>H. Lu</editor>
  <editor>S. Seki</editor>
  <editor>S. Yu</editor>
  <booktitle>Developments in Language Theory, 14th International Conference, DLT 2010, London, ON, Canada, August 17-20, 2010. Proceedings</booktitle>
  <series>Lecture Notes in Comput. Sci.</series>
  <volume>6224</volume>
  <publisher>Springer</publisher>
  <address>Berlin</address>
  <pages>209&#8211;217</pages>
  <doi>10.1007/978-3-642-14455-4_20</doi>
 </citation>
 <citation type="article" key="HarLin86">
  <author>T. Harju</author>
  <author>M. Linna</author>
  <year>1986</year>
  <title>On the periodicity of morphisms on free monoids</title>
  <journal>RAIRO Inform. Th&#233;or. Appl.</journal>
  <volume>20</volume>
  <number>1</number>
  <pages>47&#8211;54</pages>
 </citation>
 <citation type="article" key="Hon08">
  <author>J. Honkala</author>
  <year>2008</year>
  <title>Cancellation and periodicity properties of iterated morphisms</title>
  <journal>Theoret. Comput. Sci.</journal>
  <volume>391</volume>
  <number>1-2</number>
  <pages>61&#8211;64</pages>
  <doi>10.1016/j.tcs.2007.10.030</doi>
 </citation>
 <citation type="article" key="Lin68a">
  <author>A. Lindenmayer</author>
  <year>1968</year>
  <title>Mathematical models for cellular interactions in development I. Filaments with one-sided inputs</title>
  <journal>J. Theoret. Biol.</journal>
  <volume>18</volume>
  <pages>280&#8211;299</pages>
  <doi>10.1016/0022-5193(68)90079-9</doi>
 </citation>
 <citation type="article" key="Lin68b">
  <author>A. Lindenmayer</author>
  <year>1968</year>
  <title>Mathematical models for cellular interactions in development II. Simple and branching filaments with two-sided inputs</title>
  <journal>J. Theoret. Biol.</journal>
  <volume>18</volume>
  <pages>300&#8211;315</pages>
  <doi>10.1016/0022-5193(68)90080-5</doi>
 </citation>
 <citation type="article" key="Pan86">
  <author>J.-J. Pansiot</author>
  <year>1986</year>
  <title>Decidability of periodicity for infinite words</title>
  <journal>RAIRO Inform. Th&#233;or. Appl.</journal>
  <volume>20</volume>
  <number>1</number>
  <pages>43&#8211;46</pages>
 </citation>
 <citation type="book" key="RS86">
  <author>G. Rozenberg</author>
  <author>A. Salomaa</author>
  <year>1986</year>
  <title>The Book of L</title>
  <publisher>Springer</publisher>
  <address>Berlin</address>
 </citation>
 <citation type="article" key="See88">
  <author>P. S&#233;&#233;bold</author>
  <year>1988</year>
  <title>An effective solution to the D0L-periodicity problem in the binary case</title>
  <journal>EATCS Bull.</journal>
  <volume>36</volume>
  <pages>137&#8211;151</pages>
 </citation>
</bibliography>
