Assertion: progressive rock | /r/HasProperty | difficult to define
Facets:
Source sentences:
text: Progressive rock is difficult to define, because progressive rock bands often play different types of progressive rock music which sound different.
text: Progressive rock is difficult to define, because progressive rock bands are often play different types of progressive rock music that sound different.
text: Progressive rock is difficult to define in a single conclusive way, and outspoken King Crimson leader Robert Fripp has voiced his disdain for the term.