The infinite Post Correspondence Problem (ωPCP) was shown to be undecidable by Ruohonen (1985) in general. Blondel and Canterini [Theory Comput. Syst. 36 (2003) 231–245] showed that ωPCP is undecidable for domain alphabets of size 105, Halava and Harju [RAIRO–Theor. Inf. Appl. 40 (2006) 551–557] showed that ωPCP is undecidable for domain alphabets of size 9. By designing a special coding, we delete a letter from Halava and Harju’s construction. So we prove that ωPCP is undecidable for domain alphabets of size 8.
The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.
An OpenURL link contains article metadata and directs it to the
OpenURL server of your choice. The OpenURL server can provide access
to the resource and also offer complementary services (specific
search engine, export of references...). The OpenURL link can be
generated by different means.
If your librarian has set up your subscription with an
OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your
In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see
You should disable this module if you wish to use the OpenURL server that you or your library have defined.