combining user created sets

[dvanre]

What is the reason that in VEDABE I cannot make a set which is just the sum of two sets (without any other restriction), I can go round it by putting the two sets In the table, maybe it is more transparent as it is or is there another reason.

But then, if I am correct we can never make a set which includes a user defined set plus some more restrictions and this could be useful.

[AKanudia]

You can use a user-defined set in the defintion of another set once. But this new set is not available to become the part of the definition of any other set. One of the two sets you are trying to combine must already be based on other sets.