public static Backbone computeNegative(final Collection<Formula> formulas) {
        return compute(formulas, allVariablesInFormulas(formulas), BackboneType.ONLY_NEGATIVE);
    }
public static Backbone computeNegative ( final Collection < Formula > formulas ) { return compute ( formulas , allVariablesInFormulas ( formulas ) , BackboneType . ONLY_NEGATIVE ) ; }
Computes the negative backbone variables for a given collection of formulas.
@param formulas the given collection of formulas
@return the negative backbone or {@code null} if the formula is UNSAT