Task: Question Generation
Input (English): Passage: With the exception of Les préludes, none of the symphonic poems have entered the standard repertoire, though critics suggest that the best of them—Prometheus, Hamlet and Orpheus—are worth further listening. Musicologist Hugh MacDonald writes, "Unequal in scope and achievement though they are, they looked forward at times to more modern developments and sowed the seeds of a rich crop of music in the two succeeding generations." Speaking of the genre itself, MacDonald adds that, although the symphonic poem is related to opera in its aesthetics, it effectively supplanted opera and sung music by becoming "the most sophisticated development of programme music in the history of the genre." Liszt authority Humphrey Searle essentially concurs with MacDonald, writing that Liszt "wished to expound philosophical and humanistic ideas which were of the greatest importance to him." These ideas were not only connected with Liszt's personal problems as an artist, but they also coincided with explicit problems being addressed by writers and painters of the era.In developing the symphonic poem, Liszt "satisfied three of the principal aspirations of 19th century music: to relate music to the world outside, to integrate multi-movement forms ... and to elevate instrumental programme music to a level higher than that of opera, the genre previously regarded as the highest mode of musical expression." In fulfilling these needs, the symphonic poems played a major role, widening the scope and expressive power of the advanced music of its time. According to music historian Alan Walker, "Their historical importance is undeniable; both Sibelius and Richard Strauss were influenced by them, and adapted and developed the genre in their own way. For all their faults, these pieces offer many examples of the pioneering spirit for which Liszt is celebrated.".
Output (English): What did Alan Walker say had influenced Sibelius and Richard Strauss?