Looking for a clean and efficient algorithm for checking on and off elements of a “tree” (actually a DAG)?

Ah, I see why this is complicated. You want to incrementally topologically sort items as you add them to the "possibly changed" list. That way, you only process elements after you've processed their children; this ensures that you only process changed elements once, and assuming you have a DAG, you will not encounter a situation where you cannot process any elements due to circular references.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.