( ( 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 (DT The) (ADJP (RBS most) (JJ common)) (JJ two-lens) (NN telescope)) (, ,) (PP (IN like) (NP (DT the) (JJ simple) (NN microscope))) (, ,) (VP (VBZ uses) (NP (NN convex) (NNS lenses))) (. .)))