"Okay. Lemme get us an intro interworld spells book and we can go through that?"

"Sure!"

Kaylo calls up a book meeting this description without having to get out of his chair. It flies to his hand and he thunks it on the table.

Blueberry hops up onto a chair, and from there onto the table, and sits and reads the book.

Wizardry can do the following things interworld: scry, summon, and send. Scrying involves looking at things in other worlds, summoning involves pulling things from other worlds and putting them in Elcenia, and sending involves taking things that are in Elcenia and making them stop being there. Objects that are summoned or sent do not leave their relevant spells active once they've made the trip, but live creatures have "native world" as a property that continues to tie them to wherever they're from; an active summon or send must constantly work against that in order to continue working. Active summons may be broken, at least in theory (breaks are difficult); sends can't but only because their targets are not in places where wizarding spells may be cast. Active spells, if not broken, must end via either reversal or caster death.

"Sure." Kaylo gets her some paper and a graphite stick.

"As far as I know, no, there isn't any relevant concept of adjacency or distance."

"Hmm. What is there, then? What identifies worlds as different from each other but the same as themselves?"

"...good question. When we look for someone specific it's a matter of being able to identify it through a unique description or personal experience, like, I've met you, I could go serve as a focus if somebody else wanted to summon you, if I were going to send somebody to your world I could put them in your library..."

"Hmmmmm. I want something better than that," she says. "But if you can't find anything then I guess it'll have to do."

"It'd certainly be convenient if worlds had, say, ID numbers, but if they don't naturally exist I can't make a spell to 'find' them. Probably."

"They have to have something. Because they are different, so the way they're different has to exist," she says reasonably. "But it might be very hard to find out about. And it's not necessary, it would just be nice to have while I'm making my spell."

"Is it necessary that they be different in a way that is not just being contiguous with different things? Like, Elcenia is all the stuff that you can get to by moving around through space from here, and your world is all the stuff you can get to by moving around through space from your library, and the two don't hook up unless you're doing interworld magic, and that's all?"

"It isn't quite all, though, is it? There are different kinds of magic and different shapes of planets in our worlds, and there must be some kind of reason for that. Even if it's just that worlds are a type of thing that can start off in a lot of different ways that end up producing different magic and things, that's still a reason. The more I understand what worlds are, the easier it is to make a spell for moving between them. As it is... I think I can probably make a spell for moving between Equestria and Elcenia specifically, with just what I know now, which is better than not having one at all but not as good as having one that generalizes easily to different worlds."

"The magic could be significantly explained by this world not having unicorns and yours not having the wizarding reservoir... but... my theory about how dragon and vampire shapeshifting works involves there being an extra little world sort of attached to this one... I wasn't conceptualizing it as near in any sense, just magically accessible in different ways than worlds like yours..."

"Interesting. Tell me more about that? What's the theory, and why do you think it works that way?"

"...Can you keep a secret?" Kaylo asks, looking around to see who's in earshot.

"Sure," she says.

"Okay, but seriously don't tell anyone, it'll wreck everything. I've been publishing research papers under a pseudonym for several years because I'm a hundred sixty and that's adolescent for dragons and no one will take me seriously if I do it as myself. I need this theory not to be too strongly connected with my real identity yet."

"I understand completely," the six-year-old unicorn assures him.

"Thought you might. Okay, so the theory is called Lialenan matter theory and it supposes that shapeshifting involves storing our alternative shapes in a semi-dormant state in an attached world-of-sorts that I named Lialen for mythology reasons. Right now I'm in my human form, but if I stay in it for a year and never turn back to my natural one in that time, I will find after that year that my natural shape has grown and healed from any injuries it had and so on. If I tuck away physical objects - like, if I shifted now, my clothes would go away with my human shape, they wouldn't be destroyed or anything - then they'll come back when I resume the form. Etcetera. Shifting is truly instantaneous once the intention to do it is formed correctly, like teleporting or summoning is when the spell is completed and unlike any spell that actually changes a thing itself - a color change takes a tiny fraction of a split to happen, but it still takes that period of time, for instance."

"I see," says Blueberry. "That is interesting. So if worlds come in types, Lialen is a different type from Elcenia and the one where Equestria is."

"Yes. I mean, if I'm right. It's all extremely theoretical stuff. I tried summoning something from Lialen, didn't work."