MergeOperation

Merge operation between two catalogues as follows: all = source ∪ target = {x: x ∈ source ∨ x ∈ target} new = all ∖ source = {x: x ∈ target ∧ x ∉ source} obsolete = source ∖ all = {x: x ∈ source ∧ x ∉ source ∧ x ∉ target} = ∅ Basically, the result contains messages from both catalogues.