Resumen
The authors have plagiarized part of a paper that had already appeared in IEEE Transactions on Knowledge and Data Engineering, 26(4), 984?996. doi:10.1109/tkde.2013.57. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Apologies are offered to readers of the journal that this was not detected during the submission process.