<http://www.w3.org/1999/02/22-rdf-syntax-ns#first>
<http://ichef.bbci.co.uk/news/ws/560/amz/worldservice/live/assets/images/2012/11/28/121128215912_isidro_chichen_itza.jpg>
<http://www.bbc.com/mundo/noticias/2012/12/121128_mexico_mito_desaparicion_mayas_jcps.shtml>