 Complete the following phrase:  In The Oxford Encyclopedia of British Literature, Kevin Dettmar writes that Sgt. Pepper achieved a combination of popular success and critical acclaim unequaled in twentieth-century art ... never before had an aesthetic and technical masterpiece enjoyed such popularity. Through the level of attention it received from the rock press and more culturally elite publications, the album achieved full cultural legitimisation for pop music and recognition for the medium as a genuine art form. Riley says that pop had been due this accreditation at least as early as A Hard Days Night in 1964. He adds that the timing of the albums release and its reception ensured that Sgt. Pepper has attained the kind of populist adoration that renowned works often assume regardless of their larger significance  its the Beatles Mona Lisa. At the 