, 
is integer, this subproblem is fathomed by Test 3 and this solution
becomes the first incumbent. In the interactive routine, you would check
the "Fathomed" box under the "x2 = 0" node and select the "Incumbent" button
under the same node. This completes Iteration 2. To prepare for Iteration
3 you would select the one remaining (unfathomed) subproblem (by selecting
the "x1 = 0" node).