Trombone with Piano Reduction. In the archives of the Conservatoire of Prague is a copy of a sonata by Gottfried Finger for bass instrument and continuo. Frantisek Posta, solo double bass at the Czech Philharmonic, transcribed the solo part into E major for his own instrument. His orchestra colleague, professor Miloslav Hejda, arranged the part in Eb major for alto trombone and finally the composer and pianist Jaroslaw Mastalir supplied both versions with accompaniments for piano as well as for string orchestra.