State the Problem Before Describing the Solution

Today I came across the following short note on Leslie Lamport's site:

State the Problem Before Describing the Solution, Leslie. Lamport, ACM SIGSOFT Software Engineering Notes 3, 1 (January 1978) 26

The idea is that, when writing a paper, you should precisely state the correctness requirements for any solution before you present your proposed solution.  Lamport points out that this idea can also be used when writing programs.  The separation of the requirements from the solution is similar to Michael Jackson's insistence that requirements be written in terms of domain concepts rather than solution concepts.

Great Spotted Woodpecker

On Thursday morning, as I was walking through the woods from Farnborough North to Frimley, I heard a sharp chirp sound and then a black and white woodpecker flew past me and up into a tree by the path.  It was probably a female great spotted woodpecker (Dendrocopus major) as it seemed to have no red on its head.  As I walked past it played the squirrel trick of keeping on the far side of the tree trunk, but it did poke its head around several times to keep an eye on me.

Reinventing Zero (the hard way)

In a recent paper, Eric Hehner gives the following beautiful example of people reinventing the concept of zero the hard way:

In the 1991 Toronto phone book, there is a page that helpfully gives the time difference to various places in the world; to the U.K. it says "+5", and to Costa Rica it says "-1". But to Cuba it says "NA", and the legenda explains "time difference not applicable". By 1996 they tried to correct it; for Cuba it says "=", with the same explanation. In 1997 they discovered the number 0 , but they felt the need then, and still do today, to explain that 0 means "no time difference".

Not Part of the Conversation

Paul Graham is really a very good writer: he has interesting things to say and he says them clearly.  Here is an example I came across today:

On the web, articles you have to pay for might as well not exist. Even if you were willing to pay to read them yourself, you can't link to them. They're not part of the conversation.

 Exactly.

Watership Down by Richard Adams

I finished reading this to my 10-year old daughter a couple of weeks ago.  It is a wonderful read - much deeper and more detailed than the film.  The writing is beautiful and the characters  are convincing and varied.  Adams creates a believable rabbit culture with its own mythology, rather like Tolkien did but on a smaller scale.  I particularly like the way that most of the rabbits have great difficulty in understanding some things which humans find obvious, like the idea that a piece of wood can be used to float across a stream.

Next spring, one sunny morning, I am going to wake Zoe up early and together we will catch a train to Newbury. From there we will take the Basingstoke bus as far as Kingsclere, and then we will walk up onto Watership Down and there I will point out to her the places mentioned in the book.  We will walk on along the ridge to Ladle Hill and, if there is time,  cross the valley to Beacon Hill on the opposite side and then look down on Highclere Castle.