Sources

1) Source: Cosmas of Prague, The Chronicle of the Czechs "This most illustrious duke was joined in marriage to Emma, who was of a nobler origin than others... He begat two sons of the greatest talent from her, that is, Wenceslas and Boleslav." (Data from secondary evidence)
2) Source: Cosmas of Prague, The Chronicle of the Czechs "Duke Boleslav had two sons of his noble wife: the brothers Ulrich and Jaromír, pride of a fertile mother." (Data from secondary evidence)
3) Source: Cosmas of Prague, The Chronicle of the Czechs "The day of his death was February 7 in the year of the Lord’s incarnation 999." (Data from secondary evidence)
4) Source: Cosmas of Prague, The Chronicle of the Czechs "In the year of the Lord’s incarnation 1006. Duchess Emma,pearl of the female sex, weakened by a fever was freed from thesecarnal bonds." (Data from secondary evidence)
5) Source: Cosmas of Prague, The Chronicle of the Czechs "He [Ulrich] had no child of a legitimate marriage because of the infertility of his spouse, but of some woman called Božena of Krezina, he begat a son of striking beauty and named him Břetislav" (Data from secondary evidence)
6) Source: Cosmas of Prague, The Chronicle of the Czechs "In the same year, on November 9, Duke Ulrich left the earthly realms and reached the celestial." (Data from secondary evidence)