vitis merge <1st_category> <2nd_category> -o <target_category>
    This command merges two categories into one.
    The target category must be specified either as a new, unique name,
    or as the name of 1st category or 2nd category.
    Upon execution, 1st category is renamed to the name specified
    via the "-o" option, and 2nd category is removed upon completion
    of the operation. Files are moved from 2nd category to 1st category,
    subject to the following conflict resolution rules:
        - if a file with the name name and inode number already exists
          in the target location, no action is taken;
        - if f file with the same name and checksum already exists,
          the move is skipped, and all categories of the source file are
          assigned to the (identical) destination file.
