( ( of ( ( the shape ) ( of ( a ( ( doubly convex ) lens ) ) ) ) ) . )
(ROOT (FRAG (PP (IN of) (NP (NP (DT the) (NN shape)) (PP (IN of) (NP (DT a) (ADJP (RB doubly) (JJ convex)) (NN lens))))) (. .)))
of the shape of a doubly convex lens.
(ROOT (S (NP (NP (DT The) (NN lens)) (PP (IN of) (NP (DT the) (NN eye)))) (VP (VBZ is) (S (NP (DT a) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (NN convex)) (VP (VB shape)))) (. .)))