binary mekso operator: for ordered list X_{1}, this word outputs the same ordered list except the indices/subscripts have been relabelled/redefined/reindexed according to rule X_{2} (see notes).

Default behavior for X_{2}: (1) if the least index of X_{1} is less than or equal to 0, then the term which is so indexed is mapped to the term which is indexed by 1 and each subsequent entry of X_{1} is mapped so as to have the successor index of the immediately previous term (without any gaps); (2) if the least index of X_{1} is positive,
then the term which is so indexed is mapped to the term which is indexed by 0 and each subsequent entry of X_{1} is mapped so as to have the successor index of the immediately previous term (without any gaps); thus the indexing is restricted to nonnegative intergers, is compressed, and toggles between starting at 1 and 0 respectively. Other behaviors may be specified. The cultural default starting index for a list is determined by context.