"László is a Hungarian writer."
Translation:László magyar író.
Yes, it is implied. In the third person, when the statement is a noun-like clause (sorry, don't know the exact term) or an adjective, the verb "van" is omitted. And this is not optional. When it is an adverb, a location, etc. then "van" is necessary.
László író - László is a writer.
László éhes - László is hungry.
László otthon van - László is at home.
László jól van - László is well.