( ( The ( Arrow ( or ( Read Head ) ) ) ) ( ( ( indicates ( the location ) ) ( on ( ( the tape ) ( that ( ( is currently ) ( beneath ( the ( Read Head ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNP Arrow) (CC or) (NNP Read) (NNP Head)) (VP (VBZ indicates) (NP (DT the) (NN location)) (PP (IN on) (NP (NP (DT the) (NN tape)) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (ADVP (RB currently)) (PP (IN beneath) (NP (DT the) (NNP Read) (NNP Head))))))))) (. .)))
The Arrow or Read Head indicates the location on the tape that is currently beneath the Read Head.
(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.