I've been programming in CPLEX/C++ and one of my constraints has a three-index sum equality, as fallow:
constraint03{j in Vplus, o in 0..(C-o_i[j])}:
sum{(i,j,o) in Ac} x[i,j,o] = sum{(j,l,o+o_i[j]) in Ac} x[j,l,o+o_i[j]]
'j' and 'o' are the same for both summatios, it's lika one arc arrive from 'i' to 'j', with capacity 'o', and after, another arc left 'j' to 'l' with capacity ('o' + 'o(j)'), where o(j) is the offer of 'j'.
Below, the piece of my code where I tried to write this constraint: