Addition of New Constraints. The addition of a new constraint to an existing model
can lead to one of two cases.
1. The new constraint is redundant, meaning that it is satisfied by the current optimum
solution, and hence can be dropped from the model altogether.
2. The current solution violates the new constraint, in which case the dual simplex
method is used to restore feasibility.
Notice that the addition of a new constraint can never improve the current optimum
objective value.