Careful analysis of the below mentioned articles by R.-L. Etienne Barnett, published in Neohelicon, has led me to the conclusion that these contributions show extensive similarities with earlier publications, by others and by Barnett himself; see the list printed below for details. This constitutes a series of cases of plagiarism and self-plagiarism which go against the publication policy of the journal Neohelicon, its publisher Akadémiai Kiadó, and Springer. For this reason the articles in question have been retracted. I offer my sincere apologies to the authors of the original publications and to the readers that this was not detected during the submission and review process.