There could not be an edge from u to v in a DAG, if w is before v in a topological order I am trying to prove that given a DAG. There exists a valid topological  ordering that has v in front of u iff there is no path from u to v. The proof is related to the fact that reverse DFS post visit order satisfies the condition of topological order.
How do I construct a proof?
Assume that there is path $u \rightarrow v$ as well. Then we have a cycle. What does this mean in terms of topological order? Can there be such an order? Whether u comes first or v comes first depends on where you start!