However, the set of the most probable implicit predicates is predictable from the semantics of the nouns.
(1a) plausibly means Als ich angefangen habe, dieses Buch zu lesen/schreiben... 'When I have started to read/write this book...' and (2a) plausibly means eine Frage die kompliziert zu beantworten ist 'a question which is complicated to answer'.