If, however, the cost reduces so that ejj for an unused route
becomes negative, then the original solution is no longer optimal and the route in question
should be introduced. The limit for the original solution to remain optimal is, for an unused route,
a reduction in cost of ejj. Thus for square 2, 1 with an original cost figure of 6, the original
solution will remain optimal so long as the cost in that square c21 is such that: