These covers are creative masterpieces of philatelists' imagination and efforts.  Here philatelists try to get stamps of associated theme cancelled on the same FDC. Associated themes can be of various subjects. Here two or more stamps of same personality, or personality with their relatives/institutions/movements etc are got cancelled on respective dates or got jointly cancelled with the issue date of later stamp. Thus these type of first day covers generate creative initiative in philatelists adding new dimension to their collecting hobby of FDCs.