https://www.youtube.com/watch?v=08dsNvZQLPI

https://www.youtube.com/watch?v=-NosZu-m07M

https://www.youtube.com/watch?v=97Up4ETRJSA

https://www.youtube.com/watch?v=tQQBQtqxaRI

http://openaccess.uoc.edu/webapps/o2/bitstream/10609/34501/7/cdiasTFC0614memoria.pdf