As touched upon earlier, when we upgraded the spell system in the 3.0 release of FKMud, we discussed the way to best handle opposition schools. The simplest solution, though divergent from core 3E, was to go by 2nd edition preset schools of opposition. Clerics had their domains set by their deity choice, rather than selecting them, another divergent, so, why not.
As to what the opposition schools were, basically the schools oppose each other in a compass type fashion, to figure out the opposition schools, you take the one directly across the compass, plus the school one tick clockwise. (How's that for geeky?)
Doing that, you come up with the list directly above, however, which is, in fact:
Invocation: Conjuration and Enchantment
Transmutation: Abjuration and Necromancy
Abjuration: Transmutation and Illusion
Conjuration: Evocation and Divination
Illusion: Necromancy, Evocation, and Abjuration
Necromancy: Illusion and Enchantment
Enchantment: Evocation and Necromancy
Divination (which we have no Diviner's guild because, quite frankly, the bulk of high-level divination spells are things you just can't put into code.) Would only have one opposition, because of the mechanincs that actually, ALL wizards, even Conjurers, could cast "lesser" divination, ie, those of 3rd level or lower, so the advantage wasn't as big for a specialist of the school. (That, and I really think it was for the sake of hey, Johnny the Diviner can predict the future, but he lost half the offensive and and all the defensive spells off his spell list... between conjuration and abjuration, that's almost all of them.)
But wait, there's one with THREE oppositions. The only logical explanation I can come up with this is, when the move from 1st ed to 2nd ed came along, they had just made the transition from Illusionists being a stand-alone class of their own, to just being a specialty school for a regular wizard (hence, the reason for the murder of Liera in FR canon). Well, in the process, TSR wrapped a whole bunch of really GOOD illusionist spells into the wizard spell list, so Illusionists had a very potent mix of pseudo-offensive, pseudo-protective, and utilitarian spells. So, in my mind, it was TSR making a balancing decision because the other schools had a hack job devoted to them in comparison (which the move to 2nd edition, IMO, pretty much was, simply for the sake of stirring up core book sales again).
Anyway, this is a problem, if three oppositions are still the de facto on FKMud (I cannot recall, and we need to check! *nudges*). Because the spell lists on FKMud, and 3E D&D for that matter, are no longer heavily weighted for the illusionist (Phantasmal killer and Weird notwithstanding). We are subjecting the illusionists to a coded disadvantage if they are opposing three schools, and it really just needs to be a little closer to 3E.