QUES: unacceptable
ANS: Willy is taller than Bill by as much as I know a boy who thinks that Bill is taller than Dan.

QUES: acceptable
ANS: The computer is playing six simultaneous games of three dimensional chess.

QUES: acceptable
ANS: Gilgamesh may have quickly cast the spell

QUES: unacceptable
ANS:
John is prouder of having gone than John expected me to believe that he wasn't.