 When the "progressive" label arrived, the music was dubbed "progressive pop" before it was called "progressive rock", with the term "progressive" referring to the wide range of attempts to break with standard pop music formula.Music writer Doyle Greene believes that the "proto-prog" label can stretch to "the later Beatles and Frank Zappa", Pink Floyd, Soft Machine, and United States of America.Edward Macan, an author of progressive rock books, says that psychedelic bands like the Nice, the Moody Blues, and Pink Floyd represent a proto-progressive style and the first wave of English progressive rock.