Here ya go Proyecto...
Rule Book page 5
Cities and Supply: A City hex is friendly if a friendly
unit was the last to enter or pass through it, or it began
that scenario as a friendly supplied City hex. A City hex is
supplied if it is able to trace a valid Supply Path of unlimited
length from itself to a friendly map edge. A friendly map
edge is the west (dark gray) edge for the Axis, and the
east and south (red) edges for Russians. The path from a
city must be in a Westerly direction only for the Axis (West,
Southwest and Northwest), and an Easterly direction only
for the Soviets (East, Southeast and Northeast).