Complex sentence: The series used by Pierre Boulez in his "Structures 1a" is found in the sketches for "Threni", but it differs so fundamentally from the row Stravinsky actually used that its relevance to "Threni" is unclear.
Split into simpler sentences: The series used by Pierre Boulez in his "Structures 1a" is found in the sketches for "Threni". However, it differs so fundamentally from the row Stravinsky actually used that its relevance to "Threni" is unclear.