visit , this laboratory of laughter 
(ROOT (FRAG (VP (VB visit)) (, ,) (NP (NP (DT this) (NN laboratory)) (PP (IN of) (NP (NN laughter))))))
(ROOT (FRAG (VP (VB )) (, ) (NP (NP (DT ) (NN )) (PP (IN ) (NP (NN ))))))