A conflict-free replicated data type.
What is it
In distributed computing, a conflict-free replicated data type (CRDT) is a type of specially-designed data structure used to achieve strong eventual consistency (SEC) and monotonicity (absence of rollbacks).
One type of data structure used in implementing CRDT is LWW-element-set.
LWW-element-set is a set that its elements have timestamp. Add and remove will save the timestamp along with data in two different sets for each element.
Queries over LWW-set will check both add and remove timestamps to decide about state of each element is being existed to removed from the list.