Add or subtract years in a date

[A_R]

Hello. I need to add and subtract items that are not numbers nor dates. How can I do it?

To illustrate it, I have changing groups of people working on projects, so I have a first column for people originally assigned, then a second for people who left in the middle of the project and a third one for people assigned also in the middle:

[A] Original composition: “John” “Jack”
[B] Removed: “John”
[C] Added: “Jill”

(All above are linked to the ‘People’ table.)

I would like to have a [D] Current column where I can get “Jack” “Jill” as result of a formula, which should essentially work as D = A - B + C, i.e., D should contain items in either A or C but not B.

How can that be done, please?

[Justin_Barrett]

Sorry for the confusion. I misinterpreted the point of your comment.