5x12 pentomino tiling

Pentominoes

A pentomino is a polyomino composed of five congruent squares, connected along their edges (which sometimes is said to be an orthogonal connection).

There are twelve different free pentominoes. Ordinarily, the pentomino obtained by reflection or rotation of a pentomino does not count as a different pentomino.

I discovered pentominoes as a nerdy kid, probably when I read one of Martin Gardner's books based on his "Mathematical Games" columns in "Scientific American". Many of them are still available and I recommend them to anyone who has a mathematical mind (or whose children have).

The logo at the top of each of my pages is one example of a 5x12 tiling of free pentominoes and the the strip at the bottom is repeated copies of a 3x20 tiling.

Pentominoes tiled in various ways

The logo and strip are derived from the above work by a Wikipedia contributor and are used under a Creative Commons licence. See here for the gory details.

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Hard Filtering SPF

I've talked before here about SPF. To recap it is an anti-spam measure and is one we've used for a long while. It works like this. A domain, the-hug.org say, publishes an SPF record as one of its DNS records. This SPF record indicates which IP addresses will send email purporting to come from the-hug.org.  read more ...

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An Utterly Impartial History of Britain: (or 2000 Years Of Upper Class Idiots In Charge), by John O'Farrell Ever the Diplomat: Confessions of a Foreign Office Mandarin, by Sherard Cowper-Coles

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