| http://www.w3.org/ns/prov#value | - In fact, signals 4 and 8 are tightly coupled: only the calling of signal 4 (i.e., setting its lever or other control apparatus to a state in which it can clear) can drive the train stop of 8 into the clear position; even its back-to-back approach signal A6 cannot clear 8's stop, as a marker signal is said to be of a higher priority (authority, urgency) than an approach signal.
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