There are many difficulties inherent in adducing citational evidence unsupported by frequency.
( There ( ( are ( ( many difficulties ) ( inherent ( in ( adducing ( ( citational evidence ) ( unsupported ( by frequency ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (JJ many) (NNS difficulties)) (ADJP (JJ inherent) (PP (IN in) (S (VP (VBG adducing) (S (NP (JJ citational) (NN evidence)) (ADJP (JJ unsupported) (PP (IN by) (NP (NN frequency))))))))))) (. .)))
The difficulties can be overcome to support the frequency. 
( ( The difficulties ) ( ( can ( be ( overcome ( to ( support ( the frequency ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS difficulties)) (VP (MD can) (VP (VB be) (VP (VBN overcome) (S (VP (TO to) (VP (VB support) (NP (DT the) (NN frequency)))))))) (. .)))