Coalesce is an example of a snapshot-equivalence preserving operation which reduces the cardinality of a set of argument tuples.
The concept of coalescing has found widespread use in connection with data models where tuples are associated with interval-valued timestamps. In such models, two or more value-equivalent tuples with consecutive or overlapping timestamps typically are required to be or may be replaced by a single, value-equivalent tuple with an interval-valued timestamp which is the union of the timestamps of the original tuples.