The notation is unconventional, but the result is still unambiguous. If we assume the three numbers to be a, b and c. Then here, the result will be described as the sum of 2 binary numbers, where the first number, S, is simply the sum obtained by adding the digits (without any carry propagation), i.e Si = ai ⊕ bi ⊕ ci and the second number, C, is composed of carries from the previous individual sums, i.e Ci+1 = (aibi) + (bici) + (ciai) :