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I originally prepared this video as a guide for a relative of mine, but then was surprised how well it came out.

In response to a previous post, very insightfully, Steve Singer, pointed out that it is helpful to distinguish between three concepts, when talking about “interfaces” in general:

• Data types
• Capabilities
• Facades

I was recently reminded of the minimal set of project management artifacts and activities that are, in one way or another, simply indispensable.

None of this is news: all of this has been well established for at least 25 years (a quarter-century!), so I was surprised that apparently it is still not common knowledge or practice — at least not as common as one would wish for.

The interface construct in the Go language is one of its most immediately visible features. Interfaces in Go are ubiquitous, but I am afraid that the best way to use them has not yet fully been explored. Moreover, in practice, Go interfaces seem to be used in ways that were not intended, and are not necessarily entirely beneficial, such as an implementation shortcut to the classic Handle/Body idiom that hides interchangeable implementations behind a common, well, interface.

Let $G$ be a finite group with $n$ elements, and $H$ a subgroup of $G$ with $m$ elements. Then $m$ is a divisor of $n$: for a finite group, the order of any subgroup divides the order of the group.

What methods are there to connect an external (USB) drive or memory stick to a Linux box most conveniently?

In my previous post on one-dimensional heat flow, I encountered sums of the form:

$$ \sum_{n=0}^\infty \frac{\pm 1}{2n+1} \exp \left( - (2n+1)^2 x \right) $$

A plot (involving the first 1000 terms) is shown below, and looks reasonable enough. Is this curve, which forms the limit of the series, a known function?

Imagine a rod that is initially at temperature $T_1$ and then brought into an environment with a lower temperature $T_0 < T_1$. How quickly does the body cool down? When will it have reached the environment’s temperature? What is the temperature profile throughout the rod, as a function of time?

This is essentially a worked homework set: a complete, step-by-step solution of the diffusion (or heat) equation in one dimension.

Like many other people, I have struggled with git. It was obviously all very clever, but somehow inexplicably difficult and frustrating to use.

Eventually, I realized that my difficulties stemmed from three misconceptions: areas, where git did something different from what I thought it did, or different from what I was led to believe it did.

How short can a complete, competitive sort algorithm be? Less than half a dozen lines? Maybe just 3 or 4?