Like in the topic can the route of piplines go 2 through the same vertics?
That means it goes through and there is a cycle and it returns again through the same vertics and then goes on further
The text says
"More over, if it is possible to transfer the gas from the station X to the station Y (perhaps, through some intermediate stations), then the reverse transfer from Y to X is impossible." which I think means it can't but I am not sure(?)
 I would be greatfull for any help, and please no comments - "no comment" better not write at all