The only surviving complete works by Epicurus are three letters , which are to be found in book X of Diogenes Laërtius ' `` Lives of Eminent Philosophers '' , and two groups of quotes : the `` Principal Doctrines '' ( Κύριαι Δόξαι ) , reported as well in Diogenes ' book X , and the `` Vatican Sayings '' , preserved in a manuscript from the Vatican Library .
Epicurus ' only surviving complete works are three letters , which can be found in book X of Diogenes Laertius ' `` Lives of Eminent Philosophers '' , and two groups of quotes : the `` Principal Doctrines '' , reported as well in Diogenes ' book X , and the `` Vatican Sayings '' , preserved in a manuscript from the Vatican Library .