( ( A ( dashed arrow ) ) ( ( indicates ( that ( ( ( a class ) ( -LRB- ( ( at ( ( the tail ) ( of ( the arrow ) ) ) ) -RRB- ) ) ) ( ( implements ( the interface ) ) ( -LRB- ( ( at ( ( the head ) ( of ( the arrow ) ) ) ) -RRB- ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (JJ dashed) (NN arrow)) (VP (VBZ indicates) (SBAR (IN that) (S (NP (NP (DT a) (NN class)) (PRN (-LRB- -LRB-) (PP (IN at) (NP (NP (DT the) (NN tail)) (PP (IN of) (NP (DT the) (NN arrow))))) (-RRB- -RRB-))) (VP (VBZ implements) (NP (DT the) (NN interface)) (PRN (-LRB- -LRB-) (PP (IN at) (NP (NP (DT the) (NN head)) (PP (IN of) (NP (DT the) (NN arrow))))) (-RRB- -RRB-)))))) (. .)))
A dashed arrow indicates that a class (at the tail of the arrow) implements the interface (at the head of the arrow).
(ROOT (S (NP (JJ Reversible) (NNS reactions)) (VP (VBP are) (VP (VBN indicated) (PP (IN by) (NP (NP (JJ opposite-headed) (NNS kinds)) (PP (IN of) (NP (NNS arrows))))))) (. .)))
Reversible reactions are indicated by opposite-headed kinds of arrows.