"Bar can relay messages while you're in here. And … Charon's the big one, but the fact that I'm here and am accumulating power and resources with more than all of the time in the world instead of reporting this place definitely puts me in violation of the big interplanar treaties. Though I could sort of call that Charon's fault, I wouldn't be being this escalatory if I had longer timelines."

"...Charon, if he is being deathist at someone you care about - as I guess he is being due to sharing the name of a prominent psychopomp in my local mythology, can sod off.  Good luck."

"Psychopomp? Those are different. …plausibly his fault but different. Psychopomps form from dying people's responses to death, Charon … 'is death' is maybe an overstatement but only maybe, he talks like he is and he has a point. Not that I'm a fan of psychopomps either, but they're not all bad? And thanks for your well-wishes."

"Yeah, well, mythology; it gets screwy, especially when you consider the world as fiction hypothesis.  Dresden Files and Percy Jackson and the original myths and also tumblr dot com and Hades the videogame - hereafter Hadesgame - all have different interpretations of the same guy my world calls Hades who's Charon's boss and god of death...adjacent, I suppose, Thanatos does exist...Anyway where I'm from Charon's the guy with the boat that you're supposed to pay for passage across the Styx.  And then the fantasy TTRPGs raided all that mythology for names for their gods since it wasn't like there was an organized Hellenic pantheon around to complain - er, there aren't actual gods at all, I mean, like, that religion as an organization, there's actually modern-day individual worshippers.  And that's why I have any idea who Charon is at all in your context, because I was basically guessing based on that."

"That's really, really weird. If you're curious: I don't recognize any of 'Dresden', 'Percy Jackson', 'Tumbler' as an, uh, website I'm guessing, 'Hades', and 'Hellenic'. 'Thanatos' just sounds like you're mentioning death in some language that your language is borrowing from, it's matching to the prefix used in 'thanadaemon'. Which I think if you trace the original etymology basically means 'deathy death creature', because there's this class of creatures formed from death that work for Charon or so, and they get called things like 'hydrodaemons' if they're death-by-drowning, and a thanadaemon is death-by-senescence, so it got named, well, after death. People don't always settle on the most organized names. The Styx is familiar, it's Charon's river. Technically thanadaemons, which look like Charon, will sell passage, but I wouldn't recommend dealing with them. Just avoid the whole place. Which should be easy for you."

"Yeah I am not going anywhere near the D&D cluster until I actually have class levels worth mentioning, if I have any say in the matter.

"First two are series of books, Thanatos is I think the actual guy who does the death-ing so it makes sense that thanadaemons are demons that represent death...

"Hellenic is an adjective for the various ancient cultures that were where what now is Greece.  Before the Romans showed up and did their syncretization of the local gods into their pantheon, which actually produces a plot point in the Percy Jackson...expanded universe, I suppose is the best way to call it, because a whole bunch of ancient gods exist in there including the Greek and Roman ones, semi-independently, which is an interesting thing to have happen when the Roman religion insists they're the same gods, no really.

"And then Christianity happened to the Roman Empire but let's not go there, that one's Explosive Runes waiting to happen to really get into discussing because it's still a culturally-extant faith.

"And yeah, Tumblr, spelled like a thing that tumbles but without the 'e', is a website.

"Or, if you will permit a stupid meme or two, a webbed site notable for its hellsite(affectionate) status.  A trashfire disaster of web development, that people use because nobody else's social media platforms suck less even if they work more.  The rest of the big few are all scraping up everyone's personal information to sell to whoever buys."

"Selling other people's technically-consensually-disclosed information sounds a lot more infernal than poor functionality is, but that could be a translation issue, 'daemon' and 'demon' don't seem to be translating the best. And Charon's old, it would not shock me if he managed to get naming information from outworld or vice versa. Anyway, since I can't get you magic would you be okay with paid for math tutoring in money? Bar can transfer my funds to a tab for you, and you can use it to get a room here and spend time waiting for people with more shareable stuff. And there are some worlds where you can get advanced technology from Bar for them if you can pay, you might be from one of them."

"Yeah, it is; that's why Tumblr is hellsite affectionate.  As contrasted with Twitter's hellsite derogatory.  And you're right, I only have making-a-demon-daemon-devil-etc.-distinction in my language because I've played some TTRPGs that did that.  Probably not yours; 5e normally doesn't give gods statblocks.  ...Does making high-end magic items cost 'experience'?  Either way, I bet there's Some Bullshit the minmaxers have for you, if we can ask them.

"...Oh right, math tutoring.  We were doing that.  ...Money to a Milliways tab sounds fine?  I'm not sure if - Bar, do you do currency conversion?  How would that shake out in this case?  ...I'm kind of nervous about suddenly being rich...ish...because I'm getting paid in gold at material-value, let alone potentially considering how much genuinely alien coins would sell for to a numismatist, not gonna lie, even if it really would solve some problems of mine, as money-enough-to-live-on tends to do."

"If I paid you in coins I have, you would likely not be able to sell them to a coin collector because they would likely disintegrate on leaving Bar. Tabs make more sense in this case."

Griffie pokes at eir tablet and shows Jane a currency conversion. It's on the higher end of what someone without a bunch of credentials and work experience would be paid for tutoring, but not shocking.

"Oh thank goodness, I won't have to explain myself to the IRS later," she deadpans.  "...Taxmen."

Griffie blinks. "If they're doing an income tax, why wouldn't 'An eccentric wealthy person wanted a math tutor while in a bar and I was there' plus whatever fraction of income they're demanding work?"

"You have to...

"...Okay probably I'd just need to file self-employed, but the joke is that I probably won't make more money than the minimum they start making you fill out taxes at, this way, like, I do not know...nine thousand over fifty...four hundred fifty hours of math education, not from where you're starting, I think - compared to the alternate case of 'where the fuck is this money even coming from, did we even issue those bills, subpoena the bank's transaction history,' that I'd get for showing up with a few weeks' gold or silver in material value."

“…right. Fiat currency. Not really used to it, at home it’s metals or gems or bank balances.”

"We still ran our economy off the gold standard til a century ago or less - a noticeable factor in the Great Depression - and there's still goldbugs jittering around even nowadays, but, yeah.  ...Technically it's banks all the way down!  And the mint."

"Anyway. If we're agreed on payments, you were going to start with limits?"

"Right, yes, math.  Bar, would you mind keeping an eye on the time?  I'm certain I'll forget.

"Anyway, yes, limits, because you need to take a limit to formally define the derivative.

"Annnnd let me look up the formalization of limits...

"Right, so, there's your infinitesimal; my mathematicians call it epsilon.

"And the limit of a function f of x, which is to say something where you plug x into the algebra and get a number out, is...

"Well.  There's one-sided and two-sided limits.

"A one-sided limit is the value of f of x plus-or-minus epsilon, as epsilon gets smaller and smaller until it's effectively nothing - but not actually nothing; an infinitesimal amount.

"A two-sided limit is when you see if the one-sided limits agree.  Most of the time people do this rather than one-siders, but one-sided limits are still meaningful.  Is this helping any?"

Griffie is taking notes and would like to try to go through the exercises in chapter 6 of this textbook – chapter 6 is the applicable one here, yes? – with Jane watching, if now seems like a reasonable time for that. She seems to be doing a decent lesson structure so far especially compared to non-interactive options?

Huh.  She's kind of surprised, but then, it's entirely possible that teaching things the way she'd want to be taught helps Griffies learn math.

Sure, she can do that; let her grab a copy herself, and then they can do some exercises.

Attempting to reason through problems aloud reveals a lot of holes in Griffie's current understanding of the limit definition of a derivative! Let's go over those areas again, shall we?

Yeah, right, okay, so let's step back a bit, jumping ahead before you understand what you're doing is a good way to land on your face - but here are some formulas and she can demonstrate working an example of each of them -

Landing on your face in training is a good way to really notice issues with your tactics. Ey didn't expect immediate success. Watching Jane go through examples is neat. Ey tries to follow along.

Huh.  Yeah, math's not much like personal combat; there's some very big blunders you might not even notice you're making if you ever do formalized proofs of stuff, just because you started off with flawed bases.  There was a practical cataclysm of set theory when someone posited the town's barber that shaves everyone who doesn't shave themselves, if she recalls correctly.  She could probably get into the details a bit more, but it's not something she formally studied, so, more calculus?

"Practical cataclysm of set theory" sounds important but if Jane can't cover it Jane can't cover it. More calculus!

"It was basically that you couldn't define 'the set of all sets', because it's inherently recursive.  Dunno exactly what replaced it."

Anyway, yes, more calculus!

And attempting to do exercises is going better now!

Jane is probably going to want to call break on this before Griffie does, unless Jane is also notably high-stamina.