Computing hierarchies using a recursive link

Hi folks, I’ve been using Same Table Linked Records Backlinks | BuiltOnAir to try to build columns that calculate hierarchies from a recursive link. For example, if I have a column of names plus a link:

Object  | Is subclass of
Fork    | Utensil
Spoon   | Frank
Utensil |

What I want to compute is a column that looks like this:

Object  | Is subclass of | *All subclasses*
Fork    | Utensil        |
Spoon   | Utensil        | 
Utensil | Kitchenware    | Fork, Spoon
Kitchenware |            | Utensil, Fork, Spoon

I’ve been running into a big load of bugs; i.e. I parse the table and add keyed {parent, kid} pairs to a list, but for some reason I’m getting a “cannot write, there are duplicate links” error. It’s beyond frustrating! Would love to know if there’s some well-defined answer somewhere out there.