To be cautious when cross referencing

When you a save a piece of data which requires to update 2 types, because this data is what links/unlinks each other, (and you want to have direct access to the linked thing from both sides), be careful to use the right operators.

This could be helpful:

Linking "list of things"
To link:
Current thing: “set list”
Associated list of things: if “list of things”: “Add”, if “single item”: “=”
To un-link:
Current thing: “set list”
Associated list of things: if “list of things”: “Remove”, if “single item”: “= Empty”

Linking a "single item"
To link:
Current thing: “=”
Associated thing: if “list of things”: “Add”, if “single item”: “=”
To unlink:
Current thing: “=”
Associated thing: if “list of things”: “Remove”, if “single item”: “= Empty”