- mapping-catenate comparator mapping1 key value mapping2procedure
Returns a newly allocated mapping using the comparator comparator whose set of associations is the union of the sets of associations of the mapping mapping, the association mapping key to value, and the associations of mapping2. It is an error if the keys contained in mapping1 in their natural order, the key key, and the keys contained in mapping2 in their natural order (in that order) do not form a strictly monotone sequence with respect to the ordering of comparator.