Links for Pope Sixtus IV

CATHOLIC ENCYCLOPEDIA: Pope Sixtus IV
http://www.newadvent.org/cathen/14032b.htm
Pope Sixtus IV - Wikipedia
http://en.wikipedia.org/wiki/Pope_Sixtus_IV
Sixtus IV
http://www.kfki.hu/~arthp/database/glossary/popes/sixtus4.html
Pope Sixtus IV
http://www.catholic-forum.com/saints/pope0212.htm