Links:
[1] http://scielo.sld.cu/scielo.php?script=sci_arttext&pid=S0034-75152015000400001&lng=es
[2] http://scielo.sld.cu/scielo.php?script=sci_arttext&pid=S0034-75152015000300001&lng=es
[3] http://dev.scielo.org.pe/scielo.php?script=sci_arttext&pid=S1726-46342011000400017&lng=es