δx⁡(w⁡(x;a+12,b+12,a¯+12,b¯+12)⁢pn⁡(x;a+12,b+12,a¯+12,b¯+12))=-(n+1)⁢w⁡(x;a,b,a¯,b¯)⁢pn+1⁡(x;a,b,a¯,b¯).