[Desthro]

From what I understand, you can't double default with chains anyway. So you can't have skills A, B, C, with A being the main skill, and then default B from A, and then default C from B. C would ALSO have to default from A. This is true for any given set of defaults.

This prevents default "trees" since one skill bought up from default cannot be used to buy another skill up from default. Programming it is fairly simple IMHO, since you systematically have to test each skill in the set as the primary skill. (You might even test having multiple primaries, but since the default groupings are fairly limited this might be harder than necessary.)

It vastly simplifies the problem- (Capital denotes primary, lowercase denotes defaulting)

Given:
1) All skills are Average

2)
a defaults to B-1 or C-2
b defaults to C-1, D-2, or A-3
c defaults to D-1 or A-2
d defaults to A-4 or B-2

For the given set, the following are possible with one primary:
A, b:A-3, c:A-2, d:A-4
B, a:B-1, c:N/A, d:B-2
C, a:C-2, b:C-1, d:N/A
D, a:N/A, b:D-2, c:D-1

In terms of efficiency, ANY skill that can have ALL other skills default to it, is going to be the most efficient with an arbitrarily large number of points. Total Skills = 4, so any primary skill that has 3 skills defaulting to it, is likely to be the most efficient. In this case, only A has 3 defaulting skills (b,c,d) so it is going to be the optimal skill for total bonuses for an arbitrarily high number of points. B, C and D only have two defaulting skills so they tie. In this case, the total number of penalties is probably going to be a strong indicator of efficiency. B has total penalties of -3, C has total penalties of -3, and D has total penalties of -3. In this instance, for this particular set of skills, A is the most point efficient, with B, C and D tying. A tie-breaker would likely be based on which skill is the LEAST important, so if skill C is the least important, skill B would be second most efficient.

This is true for any set of skills with a single primary skill. If you add multiple primary skills for any given skill set, it changes a little bit, but is still largely the same.