 Complete the following phrase:  In a letter of King Ottokar II of Bohemia to Bruno of Schauenburg, Bishop of Olomouc dated 15 August 1277, the King referred to his allies the Opole Dukes. Since they wanted to arrange a meeting in Racibórz, he requests the presence of Duchess Euphemia of Opole and her daughter, calling a Congress to discuss matters relating to the wedding of Władysławs daughter and Henry IV. The treatments of King Ottokar II were explained in his desire to obtain the support of Henry IV and Władysław of Opole in the war against Rudolf I of Habsburg, King of Germany. According to this hypothesis, there is a proof that in the second half of 1277, there was an alliance between the Dukes of Wrocław and Opole. Among the documents issued by Władysław of Opole and his sons, was found an act who provide support for all the plans of Henry IV. This document was issued after the marriage, because there Duke of Opole called Henry IV his son-in-law, and later in 1278, was added a clause that guarantees the obligations of the Duke of Opole with King Ottokar II of Bohemia, who fell on 26 August 1278 in the 