Focus and Scope Reports@SCM is a non-profit electronic research journal on Mathematics published by the Societat Catalana de Matemàtiques (SCM) which originated from the desire of helping students and young researchers in their first steps into the world of research publication. Reports@SCM publishes short papers (maximum 10 pages) in all areas of pure mathematics, applied mathematics, and mathematical statistics, including also mathematical physics, theoretical computer science, and any application to science or technology where mathematics plays a central role. To be considered for publication in Reports@SCM an article must be written in English (with an abstract in Catalan), be mathematically correct, and contain some original interesting contribution. All submissions will follow a peer review process before being accepted for publication. Research announcements containing preliminary results of a larger project are also welcome. In this case, authors are free to publish in the future any extended version of the paper elsewhere, with the only condition of making an appropriate citation to Reports@SCM. We especially welcome contributions from researchers at the initial period of their academic careers, such as Master or PhD students. We wish to give special attention to the authors during the whole editorial process. We shall take special care of maintaining a reasonably short average time between the reception of a paper and its acceptance, and between its acceptance and its publication. All manuscripts submitted will be peer reviewed by at least one reviewer. Final decisions on the acceptance of manuscripts are taken by the editorial board, based on the reviewer’s opinion.
This work is subject to a Recognition - Non Commercial - Without derivative works Creative Commons 3.0 Spain license, unless the text, pictures or other illustrations indicate the contrary. License’s full text can be read at http://creativecommons.org/licenses/by-nc-nd/3.0/es/deed.ca. Readers can reproduce, distribute and communicate the work as long as its authorship and publishing institution are recognized and also if this does not entail commercial use or derivative work. c The authors of the articles Edited by Societat Catalana de Matemàtiques, Institut d’Estudis Catalans (IEC) Carrer del Carme 47, 08001 Barcelona. http://scm.iec.cat Telèfon: (+34) 93 324 85 83 scm@iec.cat Fax: (+34) 93 270 11 80 Style revision by Enric Ventura. Institut d’Estudis Catalans http://www.iec.cat informacio@iec.cat http://reportsascm.iec.cat ISSN electronic edition: 2385-4227