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visits member for 3 years, 8 months
seen Jul 6 at 1:50

Jul
2
awarded  Curious
May
10
revised Radon-Nikodym derivatives as limits of ratios
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Jan
10
asked Radon-Nikodym derivatives as limits of ratios
Nov
21
comment Do good math jokes exist?
I just told this joke at a conference, except I flubbed it and said it was about gears with uncountably many teeth. Five minutes later, I found two of the listeners arguing about slippage in an explicit construction they had come up with.
Oct
25
accepted Inverses of two-argument functions with respect to one argument
Oct
25
comment Inverses of two-argument functions with respect to one argument
Okay, it's clear that these don't have a name beyond "finite cyclic group generated by inverting w.r.t. one argument," so I'm going to accept this answer. Thanks for the pointers and ideas! (If you're curious, these inverses have a meaningful use: computing explicit preimages of intervals under $f$.)
Oct
25
comment Inverses of two-argument functions with respect to one argument
Cool, I hadn't made the connection to Latin squares. I did, however, notice that the notation and argument order could be improved. If we have $f_1 : A \times B \to C$, $f_2 : B \times C \to A$ and $f_3: C \times A \to B$, then the functions form a finite cyclic group generated by $f_1$ and "invert by holding the second argument fixed". (This holds for any cardinality.) I'm pretty sure it generalizes. I'm also pretty sure that I'll have to consider more general notions of inverse.
Oct
23
asked Inverses of two-argument functions with respect to one argument
Oct
10
comment Why worry about the axiom of choice?
Another fine equivalence to AC: every set has a unique cardinality. This and your first example are the main things that convince me AC is not so strange.
Aug
6
answered Hyperrectangle partition of set of overlapping hyperrectangles
Jun
9
comment Equivalent Markov Random Fields
MRFs can encode any Bayesian network, so yes, they can. It's been a while since I did any of this, but I seem to remember that, additionally, every MRF has a canonical, normalized form (as long as all potentials are nonzero) based on cliques.
Feb
20
comment What algebraic structure is suitable for representing self-referential data types?
This question should be at cstheory.stackexchange.com.
Jan
9
comment Usage of set theory in undergraduate studies
I have first-hand experience in teaching 2+2 from foundations, to an 11-year-old. The trick is to explain sets as "boxes" that contain "other boxes". (You can even use actual boxes!) As soon as the child can conceptualize a box that contains "all the finite boxes" (omega), she can come up with "infinity plus one" on her own. It involves a lot of careful wording and repetition, but it's totally doable, without scary-looking notation.
May
12
awarded  Necromancer
Apr
22
answered Set-Theoretic Issues/Categories
Apr
19
comment Can infinity shorten proofs a lot?
Technically, ZFC doesn't have induction until the axiom of infinity is added. Point against this line of argument: most mathematicians don't really work in ZFC, but in a pidgin higher-order logic with sets, in which induction is probably axiomatic. Point for this line of argument: it probably matches the audience better, who (I would guess) don't distinguish between the potential infinity of induction and the completed infinity of the naturals.
Mar
7
comment When are iterated limits of sets equal to a double limit?
Ah, of course. Then I'm looking for an analogue of uniform convergence. I'd like to do this without a measure if I can, so I don't want this to hold almost everywhere just yet. I suppose I gave the $\sigma$-algebra just in case it could help somehow. (I doubt it can, though.)
Mar
7
asked When are iterated limits of sets equal to a double limit?
Nov
15
awarded  Yearling
Nov
6
comment Fields of mathematics that were dormant for a long time until someone revitalized them
Oh, you're right. 1958 it is. My point still stands, though: programming languages, as a mathematical field, was pretty much dead until Scott, Landin and Steele revived the lambda calculus and connected the mathematics to the machines. That makes John McCarthy a forerunner, a voice crying in the wilderness... "LAMBDA!"