The student sitting to her right glances over and advises with a hint of a smile, "I don't think they let you write in your own rules."

Dairine writes at the bottom of a section, "Furthermore, there is no rule against writing anything in the margins of the handbook regardless of whether anyone will read it," and holds this up.

"Sure they do, see, it says right here," she says with a crooked grin.

"Okay, you got me. No arguing with that. I am defeated. Vanquished."

"I will be magnanimous in victory." Magnanimous is a fun word to say. "I'm Dairine; what's your name?" She closes the handbook and sticks it in her backpack.

"Kestrel. I can't believe they actually printed that. I'm going to draw all over my handbook and no one can stop me." She opens hers, previously untouched, and starts doodling birds in the margins.

"Dude, nice name! Nobody can spell mine."

"Mine's in the dictionary, which you'd think would be an advantage for spellability, and yet." She has found the page where the handbook tells her she can write in it and is covering its margins in flowers.

"Right, exactly, you can go 'Kestrel like the bird' instead of 'no, not like diary, the other way'." She looks at the pretty flowers and then does a double take and pulls out her own notebook again.

"You would be surprised how many people have not heard of the bird before they meet me! I'm a walking education."

The handbook has all of Dairine's additions and amendments seamlessly integrated, the typesetting indistinguishable from original text.

"What . . . on Earth . . .? Hey, you know how I was writing in my handbook about how it's allowed to write in the handbook?"

"...n...o? You showed me the page, you didn't write that part. Unless you have remarkably typographic handwriting. If so, nice prank, how'd you get mine too?"

"I didn't . . . do it on purpose? I just wrote it in normal handwriting in mine. You probably think I'm just completely making shit up right now but I'm not. Mind doing an experiment to prove it?"

"Sure, I'm game. What's your experiment?"

"I'm going to make another minor change--how about crossing out 'three tardies gets you detention' and make it five--and then shut the book and open it again and see if it's suddenly in the notebook font. And/or copied over into your notebook." She sneaks her phone out of her bag and takes a photo of the page, makes the edit, takes another photo, then shuts the notebook.

In the process of making all of this very visible to Kestrel she fails at keeping the phone hidden behind the notebook. "No phones in class, put it away or it's mine," says the teacher.

Kestrel is flipping open her handbook and looking perplexed. "Okay, wait, run that by me again, you're going to do what that involves looking in my handbook?" She's not on the page about tardies; she's still on the flowers she drew all over the official permission to write in the handbooks.

Dairine explains the plan again as soon as the teacher has stopped paying attention. "I think whenever I write in my notebook it changes from handwriting to typed and also shows up in yours. Which I realize is ridiculous. So I want to test it and have us both watch it happening."

"That's pretty ridiculous!" she agrees. "Okay, so what were you going to change, where should I look?"

"I changed the tardy policy from three gets you detention to five gets you detention, so if everything is normal yours should say three and if everything is whacked out yours should say five. I have pics but I don't want to take my phone out again until passing period."

Kestrel raises her hand. "Hey, sorry, I can't find the tardy policy in my handbook, can you tell me what it is real quick?"

"Five minutes late is a tardy, five tardies in a semester you get detention, same as last year."

". . ."

"Thanks!" she chirps.

And turns to Dairine and raises her eyebrows slightly. "So, either you're pranking me real good, or..."

"Or I'm editing everyone's handbooks and also the school rules, retroactively."

"I guess the question is, if it's retroactive, how do you prove it to me?"

"Do you remember me taking pictures on my phone and showing you them?"

"You took some pictures of your handbook but you didn't show them to me, and you explained what you were up to but you were whispering and I didn't hear you well enough to know what you meant."

". . . That might be the memory editing again. How about this: can you write a note to yourself, not in your handbook, that I'm about to change the rules to allow cellphones in class?"

"Sure."

She writes it on... her arm. Takes a picture of it with her phone, under the desk.

Dairine opens her notebook to the technology page and photographs it under her desk.

Cell phones, including smartphones, are permitted on campus but must be kept turned off in a student's bag or locker and may be used during class. Use of a phone in the classroom will result in a warning, followed by confiscation. Confiscated items may be picked up at the end of the school day. Personal computers other than phones are not permitted.

Second photograph, hastily hide the phone and close and reopen the notebook just as the teacher starts walking toward Dairine's desk again.

The teacher stops at a different student's desk to confiscate a paper airplane that they might or might not have been folding two seconds ago.

Kestrel's arm now says Dairine is about to do some magic, which... might be shorter than what Dairine remembers seeing her write? But when she checks the picture on her phone to compare (with no particular caution about hiding it), the picture matches the reality.

"What did you do?" she wonders. "Ban paper airplanes?"

"No, I allowed cell phones, they used to be banned according to my timestream."

Does Dairine's phone have the pictures she remembers it having? If it does, what does Kestrel see when she looks at them?

Dairine's phone lives in the new timeline where the contents of her handbook have always been what they currently are. She has two pictures of a single pristine page, no markings anywhere, no differences except in how she was aiming her camera.

Kestrel, leaning over for a look, makes a thoughtful noise and says, "I can almost imagine where you would've written on it, just from the way the pictures are focused... I dunno, maybe I'm making shit up."

"I guess if your arm got retconned then my phone would also get retconned but what the shiiiiit though. Maybe I should write in the handbook that human brains are exempt from retcons."

"Okay, but will that make it so human brains are exempt from retcons, or will it retcon you into a world where there has to be a school rule that human brains are exempt from retcons because people are going around retconning things and human brains might not otherwise be exempt?"

"I mean, empirically I am already going around doing retcons and if other people were doing it do would I even know?"

"No, but like... so you write in the handbook and then the world is the one where the handbook says what you told it to. But it's a student handbook, not a guide to the laws of magic or whatever. So what you change has to be, like... You have to write the student handbook we would have in the world where no one can retcon brains. I think. It's how I would design it, anyway." She pauses. "Can I try writing in it? I won't make the world terrible. Probably. I'll try really hard not to make the world terrible. I just want, like, better cafeteria food and more art classes."

"Go ahead, I'll watch and if it turns out terrible anyway somehow I'll put I back."

She flips through Dairine's book. "I promise if you get your memories erased I'll tell you what I changed," she adds.

Flip flip flip...

"Aha! Found the cafeteria section!"

She scribbles in tiny letters in the margin next to the chart of meal costs:

LRMA is committed to providing tasty, nutritious, affordable food to all students. All school meals will offer vegan and gluten-free options, as well as options that accommodate disclosed food allergies and other dietary restrictions.

After a moment's thought, she crosses out the chart of meal costs and adds, Cafeteria payment options are available on a sliding scale.

Before closing the book, she shows her work to Dairine for approval.

"Fantastic. Sliding scale might screw up the budget but maybe it'll just delay them on building yet more sports stuff." She tries to hold the memory of the changes actively in her consciousness the whole time Kestrel closes and opens the book again.

"I'm hoping that it'll translate to—"

She closes the book and blinks several times. "—whoa, trippy—uh, hoping it'll translate to them charging richer students more to pay for the better food. Which, I, uh, think it did? I think—I think I might remember both timelines? Trippy. Um. Okay. I don't thiiiink I caused any global catastrophes." She bounces a little in her seat. "Let's do more stuff!!! Hey, what happens if we both work on the book at the same time, like you write part of a change and I write part? —oh, um, before that, did it screw with your memory at all? Tell me what I changed."

It does not appear to have screwed with Dairine's memory at all. She remembers with ordinary human clarity what the handbook looked like before Kestrel wrote in it.

"You made there be more cafeteria options for like vegans and stuff and also made them affordable, so unless you did something else I'm immune. But I only remember the original timeline; there lots of people with dietary restrictions now? It used to be like a few percent."

The bell rings for the end of homeroom and Dairine snags her handbook back. "Oh heck, class, let's meet up at lunch and try editing something together!"

"I don't think I knew the statistics in either timeline—yeah, it's a date, see you then!"

Off she trots.

If Dairine finds the time to look up the statistics in this timeline, she will find that it's still "a few percent" but the actual numbers are a little higher, and the issue just generally seems to get more press.

That's pretty neat! Dairine does look it up but also pays attention in Honors World History and Honors English 9. She doesn't pay attention in Algebra 2 because she already knows Algebra 2; instead she does her history homework until Mrs. Whitney tells her off and then she puts away the history book and brainstorms magic handbook edit ideas because that looks more like taking math notes. Kind of ironic how telling her off got her to switch from school stuff to less-school stuff but whatever. She halfassedly pays attention in freshman bio, which is to say she reads ahead in the textbook while thinking about magic. And then it is Finally lunch time! She gets her lunch out of her locker (PB&J, apple slices, bag of almonds, and and a Snickers bar) and finds Kestrel in the cafeteria.

"Okay," she says once they're ensconced at a quiet corner table, "We were going to try making an edit together. My top two ideas are changing the section about the school nurse to mention healing potions and see if that invents healing potions, and changing the grading section to say that if you get good grades on the tests you don't have to do the homework."

"Oooh, let's invent healing potions!"

"Awesome." She flips to the page that says 'Students who become ill during the school day should see the nurse in the health office.'

"So how do we want to do this, I cross out 'see' and write 'get a' and you add 'healing potion from'? Actually maybe we should test magic edits and two-person edits separately."

"Fair... can I do the health potion edit, then, and we'll think of something else for two-person edits?"

"Fire away!" Healing potions! 

She taps her pen thoughtfully against her lips.

"Okay, I want to make really sure I distinguish magic healing potions from, like, homeopathy..."

Students who become ill during the school day should see the nurse in the health office. The nurse is authorized to excuse students from class for any issue not solved by a healing potion.

"There, what do you think? I almost want to add that students who refuse a potion for personal reasons can also be excused but that might undermine the 'they definitely work' subtext..."

"Hmm, yeah. Might want to add something about being allowed to brew your own if you have a witchcraft certificate, to make them more abundant, but let's keep it simple on a first pass."

"Yeah we can do that kind of touchup in round two." She bounces. "This is fun!"

Aaaand close book, open book...

"...no change? Uh..."

The page looks the same as it did before she wrote on it. But when she flips to the front of the book, chasing a glimpse of something strange she saw as she was opening it, there's a loading bar inside the front cover.

"Healing potions, 0%. Uh. I gotta say, I was not expecting that." She squints at the page, but can't detect any ink slowly creeping in to fill the bar.

"Huh. Either it's really slow because it has to, like, reinvent physics and then reinvent a history for that physics that still has high school handbooks, or there's something we need to do some amount of before it will go through. Maybe leave it a few hours or overnight and see if it's made any visible progress and not do anything physics-altering until then so it doesn't have to start over. And then if it's still at zero maybe we're supposed to do a quest. Wanna design the thing where homework can only help your grade not hurt it and then do that one together?"

"Yes, let's! What's this thing have to say about homework, exactly..."

She examines the handbook for homework-related passages.

There's a bunch of fluff about how assessment should be frequent, objective, integrated into the course, etc and therefore homework must be at least 30% of the final grade in every class. 

"Okay, so... the first idea that springs to my mind is that instead of all this stuff about frequent objective assessment, homework is supposed to be a no-pressure way to let the student practice the material and keep tabs on how well they're doing, so it's totally optional but you get a tiny bit of a bonus on your final grade for every homework assignment you turn in, even if it was garbage. Because something something you're practicing and seeking feedback and that's academically important. Like, I dunno, probably 5% total if you do every single one, I don't even know what the world would look like if doing all your homework was worth 30% of a school year in extra credit."

"I was thinking that any homework you do counts for a normal grade and any homework you don't do it's like it was never assigned and doesn't go into the average at all, because then if you don't want everything riding on the test you can bring up your grade a lot with homework without extra credit weirdness. But then you might get a situation where people don't turn in homework they think they'll do badly on and then fail the test because they were too scared to ask for help. Is there a way to get the best of both worlds there?"

"Hmm... everything you said but also the minimum grade on homework you turned in at all is like slightly more than passing, so if you're already sucking at everything else, homework can't possibly hurt you?"

"Yeah, that works!" She pulls out some scratch paper and writes this policy down in sufficiently professional-sounding language. "You want to do the first half or the second half?"

"Second half, why not."

Dairine carefully transcribes the first half-policy and then passes it to Kestrel.

Kestrel carefully transcribes the second half-policy, and then shuts the book.

"...I can't completely tell but I think I've got dual timeline-vision again... no, yeah, the more I think about it the more I can find the spots where it diverges, it's just pretty subtle. I guess changing the homework policy didn't affect a ton of other stuff."

"Well now I'm curious what it did change, if there's anything you can pick out. Also, while I was flipping to the homework section I remembered that juniors and seniors are capped at three AP classes per person and that's stupid, there are like twelve good ones."

"Do you want to fix that? I'm not sure I can really describe the difference, I just notice that I have some non-overlapping memories where in both timelines people are talking about homework and in one of those timelines they're way less stressed about it. But it's not all, not even most of my homework-related memories—I don't think every homework policy in existence changed, just a bunch of them got slightly more generous?"

"That makes sense. I feel like I'm starting to get a sense of how much other stuff changes for a given rule change. And yeah, I want rid of the AP cap."

"All right, let's make it happen. ...I wonder how little of a change I can help with and still get the double timeline vision thing—we should test it by having me just write like a single punctuation mark this time, or something."

"This one is pretty much all crossout but you can cross out the last word?"

"Sounds good!"

"Cool." She does her part and hands it over. 

Aaand strikethrough!

"...how do I even tell if... oh, okay, in the new timeline you weren't clear about what you were going to change. Yeah, I have double timeline vision again. That's kind of unsettling, by the way."

"Would you prefer I make the edits and tell you what I did? Personally I'd rather the double vision and it's nice to get a check on the side effects."

"Right, no, sorry, I mean—it's unsettling that in the changed timeline, it's not clear what we were changing. I'm happy to keep getting the double vision, I'll let you know if I start having a hard time tracking which reality I'm in or something. The thing that freaks me out a little is that right now I have memories of crossing out a word and not really looking too closely at which word it was, alongside the memories of working on the change with you. It's like the changed timelines can't include memories of what was getting changed, because the whole timeline gets changed, so from its perspective the thing you're changing it to is the way it always was?"

"Oh man, that is weird. I would have expected that set of memories to just not include making the change at all."

"Imagine how freaky it would've been if every time you'd ever edited your handbook in front of me I'd been like 'what, no you didn't'."

"No, I mean you'd have one set with--ohhh, yeah, from all the past edits, jeez there are too many branching timelines. I wonder if they're all real and our consciousnesses are passing memories around between them or if they're just sort of--what-ifs the magic imagined and we're in a what-if right now and someday there will be a final timeline that can't change anymore."

"Good question! I have no idea! How would we check?"