( ( A ( double ( convex lens ) ) ) ( ( is ( a ( converging lens ) ) ) . ) )
(ROOT (S (NP (DT A) (JJ double) (NN convex) (NN lens)) (VP (VBZ is) (NP (DT a) (JJ converging) (NN lens))) (. .)))
A double convex lens is a converging 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)))) (. .)))