(S (S (ADVP (BASENP (DT A) (NN year)) (RBR later)) (COMMA ,) (S (BASENP (DT the) (NN history) (NN flow) (NN paper)) (VP (VBZ is) (VP (ADVP (RB still)) (NP (NP (DT the) (NP (ADJP (ADVP (RBS most) (RB frequently)) (VBN cited)) (NN source))) (PP (IN of) (NP (BASENP (NNS statistics)) (PP (IN about) (NP (NP (BASENP (DT the) (NN reversion)) (PP (IN of) (BASENP (NNP vandalism)))) (PP (IN on) (BASENP (NNP Wikipedia)))))))))))) (PERIOD .))