Intersection is an overlap of the bar with a bar that is 3 bar earlier or further upto bar 1. Earliest intersection can occur is at setup bar 8, i.e. overlap of bar 8 range with bar 5 or 4 or 3 or 2 or 1. If it doesnt happen at 8, we look at 9, if not 9, 10 or 11 and so on (till it occurs).
so if it occurs at 8, we can count from 9 (if it fulfills countdown criteria), if occurs at 9, again CD can start fro 9 itself and so on.
Hope that clears....