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