Charlie woke to the sound of chalk on a board, a sound he rarely heard when he wasn't the one causing it.
"I see you're up. Have a nice nap?"
"Yeah. What time is it?"
"5:34 p.m. Don't worry, we're fine. I worked out something that tests possible suspects against previous criteria, I talked to Twilight and the most likely next target is Applejack. That has a plus side: she rarely leaves the farm. That same thing is a minus side: we have no way of knowing where she is at any given moment. She insisted on going back to the farm, even after I told her that she was at risk."

"We use a pattern recognition algorithm. A multivariate regression analysis along with a cluster analysis. That could tell us where she'd be at any given time if we have data on her past behavior."
"And I'm sure Twilight has some of that."

"You're… telling me… that we can predict… where they're going to strike next… with her… past behavior?"
"We think so. It'll at least tell her where she is most often."
"Charlie, I don't… think I understand. Unless… they know this too… that won't help…"
"They've known where their past victims have been to a T. Even when Lightning Dust killed Cloud she knew he was going to be in the forest. All of Golden's victims thus far have been…"
"You… mean… Lightning's victims."
"Aren't they two separate- you're saying that Golden works for Lightning? Why? She's an alicorn with exponentially more power!"
"I… don't know."

"That means that we're not looking at two killers, we're looking at a single one with astonishing manipulative capabilities! And that one is Lightning Dust! I wouldn't even be surprised if she manipulated a mathematician to do these numbers for her!"
"Here's where your brother would be useful."
"That's what I originally just wanted him to do. I didn't expect that the Princesses would pick him to raise the moon. But he seems to be good at it…"
"Anyways, Twilight, do you know offhand what Applejack's daily routine is around now?"
"Actually… yes… I do…"

~Meanwhile, at Sweet Apple Acres…

Applejack hummed a tune to herself as she walked into her barn. She's just finished the last of the day's chores though her older brother Macintosh still had work to do. Her little sister Apple Bloom was off crusading with her two friends, Sweetie Belle and Scootaloo, so the farm pony had some alone time, and she planned to spend it napping. She took the red bands off the ends of her mane and tail, laying in a soft pile of hay. Suddenly she heard a knock on the barn door. Reluctantly she got up, walking over and opening the top of the two-parted door.

"What is it? Ah was just gonna get some rest." Applejack didn't recognize the pony that stood at the door. She had an orange coat, she wore a black sweater. Her eye color reminded Applejack of her friend Rainbow, though her icy glare did not.
"Apologies for disturbing you, miss. I just wanted…" the unicorn mare summoned a magical blade and pointed it straight at the earth pony, "You to tell me who Twilight gave her magic to."
This unicorn had obviously come after the Element of Honesty for a reason. If you don't want to be lied to, Applejack would be the first pony to go to.
"Ah- Ah'm afraid… ya've got the wrong pony… um… Ah've got no idea what you're talkin about…"
"Oh. I see. You know, miss Element of Honesty, you are the most terrible liar I have ever met!" She hissed, "Now tell me where the Princesses put their magic!"

"She said she doesn't know. Leave her alone." An alicorn in a cloak pulled out her own magical blade and pointed it at the unicorn. She threw her head back, flipping the hood off her cloak. She glared at the unicorn.
"P-P-Princess… Twilight? B-B-But… you aren't… you can't be…"
"Sorry to disappoint. Now leave my friend alone before I decide to put this blade to good use."
"Y-Yes, Princess!" And with that the unicorn ran off.

The alicorn turned to Applejack. "Are you all right?"
"Yeah. Twilight, is that really you?"
"No," the alicorn transformed suddenly, her purple coat changing color and her hair restyling itself, her wings becoming slightly transparent magical ones, "But I am getting better at transformation spells."
"Hey, ya're that programmer pony Twilight was talkin about! Amita, was it? Pleasure meeting ya!"
"Yes. Pleasure is all mine, miss Applejack."
"Shucks, ya can just call me Applejack. AJ, even. If there's a pony who likes goin' by 'miss', that'll be Rarity, not me."
"All right, Applejack."

"Hey, Chuck? That algorithm of yours worked. Not sure how you did it, but Twilight sure made a good decision with you." Rainbow hovered around the room, cleaning books off the floor.
"It's a simple pattern recognition algorithm. It won't solve the problem forever, but it'll solve it for now. I'll have to get to work on a predictive analysis if I'm going to predict the rest of these attacks. The next target would have to be Rarity if they now think that Applejack is too much of a threat. They'll certainly come back to her though, these ponies seem fairly determined."
"I didn't just stop by to help you clean these books up, ya know."

"Then why'd you come?"
"I was flying earlier and I recognized the pony from one of Rarity's sketches, name's Golden Tiara, she was in a blue vest that she'd obviously had for a while, several seams were popped, though it can't have been of too much value 'cause she has a lot of money and could've gotten it replaced if she wanted to. The vest covered her magical wings almost entirely, though if somepony was looking they could've seen a wing-tip. That and the fact that the vest was fairly loose made it so I couldn't really make it out, but I think her wings are yellow like her aura and they're shaped similarly to Princess Luna's. Golden was leaving a weapons shop with a plastic bag, given how much the bottom of the bag was sagging I'd say that she was carrying a bow, arrows, a small dagger… and a club."

"You know all this just by flying by?"
"Yep. Oh, and I have a few… theories I guess you eggheads call 'em. First off, she didn't bother to disguise her wings, meaning that was the only stop she planned on making. However, she had a few dots of whipped cream on her face, meaning that she stopped for a milkshake before. It's… what, probable? Yeah, that's it. It's probable that she got a vanilla milkshake. That's cause I didn't see any different colored dots on her coat and vanilla is real close to whipped cream colored. Second, she obviously hadn't eaten much that day, so I think she was on a mission of some kind. A pony as rich and pampered as her wouldn't just forget to eat. Third, she was meeting with somepony that she didn't want to be seen meeting with. I saw her looking around cautiously while she trotted kinda fast."

"That's… impressive."
"Nah, not compared to you. You know, I heard you were some kinda genius? Yeah, Twi said something about that. I didn't believe her at first, but given all this stuff…" she gestured to the blackboards, "I do now."
"It's not that complicated."
"Yeah? Best I ever did with math is solving for x. I don't do all these weird symbols." Rainbow flew over and pointed a hoof at one of the symbols. She turned to Charlie, waiting for an explanation as she hovered by the blackboard.

"They're letters. Greek letters, specifically. The other ones are operatives. It's all just multivariate regression and cluster analyses. As for the latter… let's say I'm taking a survey. I look at lots of variables: whether it's a pegasus, unicorn or earth pony, what their favorite color is, their coat color, their hair color, et cetera. From that I can figure out that, say, a unicorn's horn aura is either the main color in their cutie mark or their eye color. But if I want to see which ponies are similar to others, I'll want to have the ability to make them into clusters. That's what a cluster analysis does, a cluster analysis in n dimensions is using n to describe the amount of variables." He pointed to several of the blackboards. "These are cluster analyses. Multivariate regression is a little more complicated, but that's this over here."

"Okay then. I can see why the ponies back on your world like you."
"They're not ponies on my world."
"Okay, then I can see why the things back on your world like you. Thanks Chuck."
"Did you get that from Don?"
"Who?"
"Forget it. It's just that everybody- everypony loves calling me that. Anyway, thanks Rainbow."
"No prob. Anytime I can be of use. You need any help with some more cluster thingamabobs, let me know."
"Don't worry, I will."
Rainbow was flying out the door when Charlie asked, "Hey Rainbow? Can you do a cluster analysis on… this?" He held up a sheet of paper with his magic.
"Sure thing!"

Rainbow flew over to one of the empty blackboards. She looked back and forth from the sheet to the board as she took a piece of chalk in her teeth and began writing.
Charlie was astonished. She seemed to have memorized the notation. And, the processes required to perform one of these. For somebody who only got through algebra, she seemed to be a quick learner. And a natural at math.
Still with the chalk in her teeth she flew over to him and said, "Done!"
"You think you could learn how to do regression this quickly?"
"Nah. I don't really like math. I prefer flying. I'm more of an athlete, though your occasional nerdy thing can get through to me. Occasionally."
"You're this good at math and yet you don't like it?"
"Nope. But you were watching me fly yesterday, how was it? Was it totally awesome?"

Realizing he couldn't get through to her, reluctantly he let her leave. If he only could have taught her one thing, cluster analyses wouldn't have been it. True, they're useful, but not nearly as useful as several other concepts. He sighed and turned away from the door, beginning to work on the predictive model he'd been wanting to work on.
The door opened. "Charlie, you were right. Applejack was the next target. And you were right, she was in the barn when the attacker came."
"Were you right that you could fend them off by impersonating Twilight?"
"Yeah. Only bad news is that the unicorn ran off before I could ask her who she's working for and how she got that location."

"I just heard from Rainbow Dash that Golden Tiara was buying weapons earlier today. A bow, arrows, a small dagger and a club."
"I didn't recognize this unicorn. Her cutie mark was something like this…" Amita drew a right triangle, labeling the hypotenuse 'x' and the vertical side 'y' as well as labeling the acute angle of the hypotenuse and base 'θ'.
"I think we've found our mathematician."