I have DAG. I can then define a proper subgraph from some set of nodes {A, B, C, ...} such that the subgraph contains all transitive dependencies of that set of nodes. Given two sets of nodes X and Y, I want the set difference between the subgraphs of nodes defined by X and Y (and all of their transitive dependencies). So, what nodes exist in the subgraph of X but not in Y, and vice versa?

Ie, if we have the graph { A -> B, A -> C } then the diff between {A} and {C} is ({}, {C}). And the diff between {B} and {C} is... well, ({B}, {C}).