InsaneJournal

Tweak says, "Easier than eating turnips."

Gideon finished off the last few notes of the sonata he was practising--one of their mother's--while Fabian did something that would have been sitting on the sofa except that his head and shoulders were down where his knees should be and his lower legs were dangling over the back of the sofa. He had his work in hand and was reviewing his higher maths and not liking the answers he got.

Before Gideon could start his next review of the piece, Fabian shoved the paper in his general direction. "I want you to review my arithmancy on this and tell me if I've totally bollocksed it up or whether these terms really don't balance properly." He'd been working on Dumbledore's oath for several days and there was something amiss with the terms.

"All right, give me a moment to engage my maths brain. The Chief Warlock was a genius, I think, which is not good for us non-geniuses who have to decipher what he's enciphered. I spent four hours this morning researching someone named Pierre de Fermat, who lost a theorem for 400 years or so. Careless bloke. All because of one footnote in those papers."

Gideon pulled on his reading glasses. He didn't need them to see, but they did let him make notes and notice certain magical things more easily. "OK, so every place it says 'Quod Erat Demonstratum' I feel like I've lost a class year and need to repeat it for credit. His Demonstratums are so often undemonstrative." Gideon took a quill and quickly jotted some additional formulae in the margins. "Take this one. I can transform the equation back to being Aelred Sillem's first theorem from the Quarr Abbey Grimoire, except there's a constant here for the radial value of the latitude of the caster and a variable for the change in magical energy over time. I don't know any case where either of those matter. Or how he proved that it was obvious that those factors are needed. Or why you'd even make a point to use a negative value inside of absolute values, since that negative isn't reflected elsewhere, except maybe it is."

Gideon pushed the paper back towards Fabian, upside down. "Near as I can tell, the equations are wrong because the signs of this formula, which shouldn't matter, are double negated, but it means something in some other case. I think we need to both check the first and second order derivatives and also think about this as music. What if what the Chief was doing was more akin to musical harmonics than mathematical equivalences? What if simplifying the equation inherently makes it less accurate?"

"Demi-Euclidean calculus will always be my bane. This is why I didn't ever consider Mysteries." Which was a lie, but the sort of outrageous lie that sounded better than the truth. "Or, you know, he could have just buggered it up and there could be a flaw."

It was something of a heresy to suggest that Albus Dumbledore had made an error, but Fabian was well-known for turning sacred cows into minced meat. "I mean, it could be, right? Just--as a possibility."

Gideon nodded. His brother's heresies were often more accurate than most people's orthodoxies, and always worth considering. "It is a possibility. Except that primus, the spell worked and secundus … I don't have a secundus. Does it weaken the compulsion? Lengthen the spell? Change the conditions? Alert the Secret Keeper if the oath is violated? Automatically teleport the Secret Keeper to Minorca for a holiday if they are about to die?"

He waved his quill in small circles. "I can't tell. I hate to be 'that wizard', but we may need to conduct a series of very dull experiments."

"I say we're in for some dull experiments. Because the Headmaster might be a genius but he's fallibly mortal just like the rest of us. I mean, presuming the reason the oath hasn't failed is something I haven't anticipated, like--he had that book about the H-thingummies in his office for a very different reason that Professor McGonagall suggested." Fabian's tone left little doubt that he thought that wasn't the case and he was simply being the Centaur's Advocate.

"Who knows? Maybe his entire life was penitence for something truly awful he did to Merlin as a fifth-year, in the 13th century…" Gideon appreciated his brother's comment. "Even if it's a cockup, I would love to have a variety of different unbreakable oafs available to the Wizengamot."

Fabian rolled down and righted himself on the sofa. "There are already a ton of unbreakable oafs in the Wizengamot. Merlin's sweaty ballsack, look at Oscar Macnair. On the other hand, we haven't really tried to break him yet." He made a face. "Anyroad, about the oath: I believe in irrational numbers but they do represent weaknesses that can be exploited. And if it's possible there's a weakness, we need to assume someone can and will do the exploiting. So we work out a test bed and do the testing. It may take a while but it's almost as important as the horcruxes."

Gideon agreed, about Macnair and the oath. "Macnair is the subject of a quiet word between the clerk of the docket and the Chief Wizard that he should not be allowed to hear cases where one party is a Scot, because he believes them all to be guilty … of Scottishness, apparently."

Fabian rolled his eyes.

Gideon continued, "As to the oath, I can devise a battery of tests, and we just need some test subjects for one of us to lie to. Charlie and Bill? It's cheaper if we can pay in candy than beers…"

"Molly will kill us both if she catches us. If the boys fall through, we talk to Fi and Alix." They were dependable and Fabian knew they knew how to keep a secret. Certainly if they suspected his outside efforts, they'd never said so much as a word.

Gideon was already scratching down an series of tests. "I apologize in advance if this testing turns your hair white; it's in the name of science, and not having everyone we love killed. It should be temporary. Maybe purple."

Fabian gave his twin a resigned shrug as he picked up another sheet of parchment and a biro. "Better than my first thought, which was saying SNEAK in spots all over."

Gideon reached over and drew an X on Fabian's paper. "I'm not sure you can get Fi and Alix to cooperate with us if your plan involves defacing our pretty face, and I say that as the emergency backup twin in that relationship."

"I abandoned the idea because I didn't want to wreck either of their pretty faces. Or have either of them wreck mine."

"Certainly not by accident, no," Gideon agreed.

Fabian snorted. "And anything else, you're not invited as backup for."

"Girls can get awfully lonely when you're off with your respectable friends. Don't assume you know everything, old bean."

"i'm sure he'd be insulted if he knew you were calling him that," Fabian mock-complained on the gentleman in question's behalf.

"I'd never let him know I respect his reputation. He's too fragile for such knowledge."

Fabian stuck out his tongue at Gideon. "Maybe you should. It'll just make me more enticing."

Gideon frowned, suddenly not in a joking mood. "I've always wanted to assume he was just too fundamentally unserious to be on the other side. I hope I haven't credited him too far. His brother and father, and certainly his sister-in-law, are a different story.

"Do you think they pose a risk to you because they don't like your association with him? It would be sad to be defenestrated without a wand as an object lesson to your friend."

Fabian turned to look at Gideon full on. "I hope 'Dolly' and 'Trixie' think I'm too fundamentally unserious, not to mention too much of a coward, to be a threat to anything Rabbit may be up to. But trust me when I say that of the three surviving Lestranges, Rabastan may well be the most dangerous."

It was either a show of faith in his brother or a desire not to rehash ancient differences that kept Gideon from arguing the point. "Then we best get on with our research, and hope the search team gets on with theirs."