• "Differencing" method not working

Question related to mission Loading Cargo

 

Can this problem be solved with the "differencing" method? I've gone past by the 5th example, but got stuck with 6th - checkio[1,1,1,3] returns 2 as the lowest discrepancy (1-1=0, 3-1=2, 2-0=2), although it is obvious that it should be zero.