"#ff0000"> location </font>to another along a <font
 color="#ff0000">track</font>.&nbsp; The track segments form a directed graph
and are connected by a <font color="#ff0000"><i>next segment<sub>n</sub>
segment<sub>n+1</sub> </i></font>relationship. The track is single track
and only one tracked mobile can occupy a segment of track at a time. A track
segment is either <font color="#ff0000">occupied</font>, if a mobile is "on"
the track segment or it is <font color="#ff0000">free</font>.<br>
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