may not add up to the sum of its parts 
(ROOT (S (VP (MD may) (RB not) (VP (VB add) (PRT (RP up)) (PP (IN to) (NP (NP (DT the) (NN sum)) (PP (IN of) (NP (PRP$ its) (NNS parts)))))))))
(ROOT (S (VP (MD ) (RB ) (VP (VB ) (PRT (RP )) (PP (IN ) (NP (NP (DT ) (NN )) (PP (IN ) (NP (PRP$ ) (NNS )))))))))