Pablo Ximenes, André Santos, Marcial Fernandez, and Joaquim Celestino Jr.. 2005.
 A Proposal of Human Interactive Proof in the Text Domain. In <em>Proceedings of the 5th Brazilian Symposium on Information and Computational Systems Security</em>, September 26, 2005, Florianópolis, Brasil. SBC, Porto Alegre, Brasil, 36-39. DOI: <a href="https://doi.org/10.5753/sbseg.2005.21543">https://doi.org/10.5753/sbseg.2005.21543</a>.