Things are mutually exclusive within a table, but not later

[Mathias]

Here's what I'm trying to enter:

A thing adds the following:
Skill A
Skill B
Skill C or Skill D
skill E or Skill F

a different version of the same thing adds:
Skill A
Skill B
Skill C
Skill D or Skill E

I've got the fixed skills working (bootstrap them with an autotag that tells a <list> statement to show them in this table as well as the general skill table).

I can generate a candidate tag expression (placed in a herofield) that correctly offers skills C-F in the first case, or skills D-E in the second case. My problem is getting it to keep the user from selecting both C and D.

I've tried writing a candidate expression checking the count of a tag, I've tried a denytag expression (please add more description to the needtag/denytag section of the wiki).

I know a pre-req could prevent one item from being selected if the other was selected, but it's legal to buy the skill(s) not taken later in character creation.

I could also get around this by having multiple choosers, but I think it looks better to display all the skills granted by this thing in one table.