Prove that a flow graph is reducible if and only if when we remove all the back edges (those whose heads dominate their tails), the resulting flow graph is acyclic. A complete flow graph on n nodes...

Prove that a flow graph is reducible if and only if when we remove all the back edges (those whose heads dominate their tails), the resulting flow graph is acyclic.

A complete flow graph on n nodes has arcs i -> j between any two nodes i and j (in both directions). For what values of n is this graph reducible?