Clive D. W. Feather wrote:

In article , Arthur Figgis
] writes
but would the two lines have to be joined to constitute a network? The
mathematical types I know weren't sure.

From my rather rusty memory, it depends entirely on context. Some
theorems on networks require them to be connected (i.e. ignoring
directional arrows, there must be a path between any two points in the
network) while others don't.


From a completely non-mathematical POV the Dublin tram system could be
a considered a network as it is operated by the same organisation, and
(pls excuse my ignorance) I presume to some extent the two lines share
staff (drivers, PW and rolling stock engineers/mechanics), other
facilities (such as maintenece kit and depots), a ticketing system etc
etc

So thare other elements in the system that are interconnected although
the track is not.