artist-prev-next-op-alist is a variable defined in `artist.el'.
Its value is

Assoc list for looking up next and/or previous draw operation.
The structure is as follows: (OP . (PREV-OP . NEXT-OP))
where the elements are as follows:
* OP is an atom: the KEY-SYMBOL in the `artist-mt' structure
* PREV-OP and NEXT-OP are strings: the KEYWORD in the `artist-mt' structure

This variable is initialized by the `artist-make-prev-next-op-alist' function.