Difference Sign on the Model

Hello everyone;
In the gams model, how can i write the difference on the set (l is element of C{j}) as attached photo.
20220305_170430.jpg
Is the following code sufficent for that??

sum((i,j,l)$(ord(j) ne ord(l)),alfah*d(j,l)*g(i,j,l))

That depends on the content of your sets. Maybe the sameas operator could be helpful.
It would certainly be easier to help, if you would share an example based on actual GAMS code.

Best,
Fred