Fall to and Set upon

Fall to verb - To take the first step in (a process or course of action).

Set upon and fall to are semantically related. In some cases you can use "Set upon" instead a verb "Fall to".

Set upon verb - Assail or attack on all sides: "The zebra was beset by leopards".

Fall to and set upon are semantically related. Sometimes you can use "Fall to" instead a verb "Set upon".