I have a long-time collaborator who lives in Georgia (I’m in Pennsylvania). I’ve had good luck collaborating with him via email, but it is a pain. As soon as one of us edits a file he sends it to the other person as an email attachment. We haven’t had any “forked” files, but we do…
Bolzano-Weierstrass Rap
In my next real analysis lecture, we’ll be discussing the Bolzano-Weierstrass theorem. (It says that any bounded sequence of real numbers contains a convergent subsequence.) I’ll be showing my class this video in which Steve Sawin (AKA Slim Dorky) raps the complete proof of the theorem. You can read the lyrics here. He has some other…
Is or an inclusive or or an exclusive or?
(That was a fun title to write!) At the start of our discrete mathematics course we talk about symbolic logic. Students are often confused by the logical operator “OR.” If p and q are statements then p OR q is true if either p is true or q is true or if both p and…
An applet for teaching the limit of a sequence
I’m currently teaching real analysis. Right now we’re discussing limits of sequences. The definition is: The limit of a sequence is (or converges to ) if, given any , there exists a natural number such that for all . I used GeoGebra to create the following applet, which illustrates the definition of a limit. (Clicking…
LaTeX now available in Google Docs
Google Vice President and Chief Internet Evangelist (yes, that is really his title) and inventor of the internet Vint Cerf visited our campus a couple of years ago. At one point he asked about what people wanted from Google. I said that I would love a Google Docs/LaTeX mashup. How great would it be for…
The nuts and bolts of writing mathematics
This was a handout that I made for my Discrete Mathematics class. At our college this course is the gateway to the mathematics major and is the students’ introduction to writing mathematical arguments. Here is a pdf version of the text shown below. The nuts and bolts of writing mathematics “Mathematics must be written so that…
Cardinality of infinite sets, part 1: four nonstandard proofs of countability
The study of cardinalities of infinite sets is one of the most intriguing areas of mathematics that an undergraduate mathematics major will encounter. It never fails to bring crooked smiles of joy, disbelief, confusion and wonder to their faces. The results are beautiful, deep, and unexpected. Recall that two sets have the same cardinality if…
Casting out nines
It is now 9:09:09 on 9/9/09.
Mathematical spellcheck fail
I love my Macs, so it pains me to post this. All three of my Macs think that “Pythagoras” is a misspelling. That fact doesn’t bother me—there are a lot of proper nouns missing from the spellcheck dictionary. What hurts is that the spellchecker suggests Pythagorus as a correction. See screenshot below. C’mon Apple! You’re…
Symbolic dynamics for nonhyperbolic systems
I suppose the intersection of people who read this blog and people who are interested in my research is, if not zero, close to zero (come to think of it, the set of people interested in my research is not much greater than zero as it is). But I thought I’d mention that my collaborator (Jim…
David Richeson: Division by Zero 