If the flag is true, {TAIL ~ the OptionalSort operation} changes the order keys of {HEAD ~ elements} in the dataset 
If the flag is true , { TAIL ~ the OptionalSort operation } changes the order keys of { HEAD ~ elements } in the dataset
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH