No problem! I hope people realize that transferring an H-1B is actually not that complicated. It sure made me feel a lot more confident about switching jobs.

Always wanted to see something like this! Hope it'll get referenced a lot on resources like Mathworld or Wikipedia. Love the extensiveness!

Dumb question maybe, but is knowledge like this often used in symbolic solver software? If so, would it be useful to implement examples in a programming language like Gerald Sussman did in Structure and Interpretation of Classical Mechanics?

I've been working on a symbolic solver lately and have had to implement a lot of techniques manually. I'm not aware of any machine-readable database of solving techniques (which would be great for this, especially for integrals, because right now my code doesn't know any integration techniques that I don't know myself).

A lot of big solvers use algorithms[0] that can't always be reduced into a reasonable series of steps for producing nice step-by-step output, which is why e.g. Wolfram Alpha will occasionally manage to symbolically integrate something but tells you that a step-by-step solution is unavailable. (This happens even with plain algebra; Wolfram Alpha can explain how to derive the quadratic equation but not the cubic.)

Could you elaborate more on the nature of the examples from this book for those of us who haven't read it?

[0] Risch algorithm, Gaussian elimination, etc.

Hi, that's indeed our old sensor which is composed of two AIR sensors. The new sensor carries a slight upgrade in hardware, but the real power comes from our signal processing. See my reply to thwest here. https://news.ycombinator.com/item?id=9879671

So you use 2 different IR sensors, which "measure your circumference to some degree" and provide a "distance profile" which somehow translates into real-time accurate foot traffic counts. IMO that's definitely a cop-out explanation, and per usual, there is not any actual quantification.

When you would wear metamaterial stealth suits maybe you can avoid being detected by our IR sensors, we're curious as to what you have available!

Incredibly accurate and anonymous seem to be at tension here. A discussion on your signal processing would be illuminating.

We made our own AIR door counter, composed of a few distance sensors. It can tell us in which direction a person is passing, and gives a distance profile that we process to distinguish individual people. Technically, we measure your circumference to some degree, but you might agree that is far from enough to compromise your anonimity.

AIR being active infrared as opposed to passive (or a particular waveband)?

Anonymity is a more interesting problem than "can distance sensors uniquely identify a passerby among 500M North Americans" as your reply implies. What if you are the roundest or tiniest person in town? All the sudden you are uniquely identifiable.

You're early in development, and I bet whoever did the circumference estimation has more in mind. I imagine you could make a good estimation of a person's height from your data: whether the profile sees knees hips or hands. Can you identify the asymmetric waist bulge of a CHL carrier? Does your infrared band penetrate polyesters but not cotton? I hope the reader's feature-vector blood is flowing at this point.

Your page needs to have way more formalization around the concept of anonymity (outside of the registration required area) for me to feel that you are appreciating the problem from an engineering perspective and not a marketing one.