At each iteration, the set of the redundant sentences of Y is calculated and the costliest one (according to the cost function C) is removed from Y.
an element s of Y is said to be redundant if for each u i ∈ U, its number of instances into Y, denoted m i (Y ), and into Y \ {s}, denoted s is a redundant element of the covering Y if Y \ {s} is also a covering solution of Equation (1).