once in a blue moon , listed under moon in L ) may be listed elsewhere (under blue moon in W).
( ( once ( in ( ( ( a ( blue moon ) ) , ) ( listed ( under ( ( moon ( in L ) ) -RRB- ) ) ) ) ) ) ( ( may ( be ( ( listed elsewhere ) ( -LRB- ( ( under ( ( blue moon ) ( in W ) ) ) -RRB- ) ) ) ) ) . ) )
(ROOT (S (NP (NP (RB once)) (PP (IN in) (NP (NP (DT a) (JJ blue) (NN moon)) (, ,) (VP (VBN listed) (PP (IN under) (NP (NP (NN moon)) (PP (IN in) (NP (NNP L))) (-RRB- -RRB-))))))) (VP (MD may) (VP (VB be) (VP (VBN listed) (ADVP (RB elsewhere)) (PRN (-LRB- -LRB-) (PP (IN under) (NP (NP (JJ blue) (NN moon)) (PP (IN in) (NP (NNP W))))) (-RRB- -RRB-))))) (. .)))
The phrase "once in a blue moon" may be listed elsewhere. 
( ( ( ( ( The phrase ) `` ) ( once ( in ( a ( blue moon ) ) ) ) ) '' ) ( ( may ( be ( listed elsewhere ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN phrase)) (`` ``) (NP (NP (RB once)) (PP (IN in) (NP (DT a) (JJ blue) (NN moon)))) ('' '')) (VP (MD may) (VP (VB be) (VP (VBN listed) (ADVP (RB elsewhere))))) (. .)))