Back up and Hark back to

Back up verb - Move backwards from a certain position.

Hark back to and back up are semantically related In some cases you can use "Hark back to" instead a verb "Back up".

Hark back to verb - To bring back to mind.

Back up and hark back to are semantically related in return topic. You can use "Back up" instead a verb "Hark back to", if it concerns topics such as go back.