The street from A to B which, if entered, there is no way back to A.
A crossing is weak if at least one weak street begins there.
All streets begins here are not weak.
A sequence of streets a truck passes from A to B.
- passes only through strong crossings
- passes through minimum possible number of streets
Another crossing Y is a target for X if there is mutal strong connection between X and Y.
The number of targets of X
Let crossing Y be a target for X. The cost of Y is a number which is equal to twice the length of the strong connection from X to Y plus the length of the strong connection from Y to X.
Is equal to the sum of the costs of all targets for X.
Is a strong crossing which variability is maximum and its cost is minimum among all strong crossings with maximum variability.