The paper is based on 3-way merge of relations (sets) but I'm not sure it's uniquely defined. Imagine we have a data structure consisting of two sets A and B, w

The paper is based on 3-way merge of relations (sets) but I'm not sure it's uniquely defined. Imagine we have a data structure consisting of two sets A and B, with the invariant that B is a subset of A. Initially A = {1}, B = {}. Imagine this data structure is replicated across two computers. On the first computer, we add 1 to B; on the second computer, we remove 1 from A. Then we try to merge these changes. It seems that the merge result could be either A = {1}, B = {1} or A = {}, B = {} and I don't see how to choose between them.