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You should enter this web site by using the URL (or alternatively, or If you bookmarked a different URL, please change your bookmarks to one of the above URLs. Any other URL may be temporary, and may change without notice. Individual pages within this site can be reliably bookmarked after entering this site through one of the above URLs.

Please note that parts of this site may be hosted at different Internet locations, and that their geographical locations may change at any time. The URLs above are the only permanent way to reach my web site.


I used to display ads on my pages, albeit not currently - it simply does not generate enough money to have any practical impact, takes space on the pages and is distracting to visitors. If you see any ads on my pages at present (other than in the Google site search popup), your ISP is adding them, or you have malware on your computer that does so. Alternatively, you may be visiting my pages through frames of another site. In this case, use one of the above URLs to visit my site instead.

The site search functionality on the home page of this site is provided by Google. Google may choose to display ads in the popup that contains the site search results. I have no control over the contents of these ads or their relevance to the contents of this site, and I don't endorse any of the linked sites in the ads.

Updated and changed contents

I usually indicate new pages with a icon in index pages. Usually, this icon remains until the next major addition of new pages in the same section of the web site. I also update pages whenever new information is available, or whenever I discover errors. Updates happens fairly often for pages of this site, and may range from the correction of misspellings to major additions and/or alterations of contents.

I mark updated pages with an icon only if the changes are substantial (e.g., major errors have been corrected, or significant materials have been added). The best way for you to know when a page was last updated is to check the "last updated" file date in the footer of each page. This is actually the date the file was last saved on the server, so it may reflect a change in contents, or only cosmetic changes to the layout (for example updates in order to function with current browser versions), or changes of my web authoring tools.

Required web browsers

This web site requires a modern web browser (e.g., Firefox v 38 or later, Microsoft Internet Explorer v 11 or later, or equivalent browsers). This site requires JavaScript, does not function properly without it, and no longer attempts to display a warning if JavaScript is unavailable. HTML 5 makes JavaScript obligatory, and this site now conforms to several HTML 5 requirements in order to remain future-proof. Pages containing Java applets additionally require a working Java runtime system, and will not work on mobile platforms that do not support true Java.

I have tested, and found the current version of this site to work, with Firefox version 51.0.1. Other versions and other browsers may work, but are not tested.

In 2015, I converted this site to a mobile-friendly format.

The appearance of this site is mostly unchanged for visitors using a large screen, but the new layout is simplified with respect to the older one, particularly for what regards illustrations. The visible changes affect mostly users of tablets and smartphones:
Figures automatically resize to fit the screen width.
Figures are linked to the original image file, to allow viewing at the original size on all devices (this may require scrolling and zooming on small screens).
Two-column and three-column layouts become one-column layouts on small screens.
Navigation buttons become larger and more widely spaced on small screens, to allow operating with fingertips.
Groups of navigation buttons rearrange on small screens, to avoid horizontal scrolling.
Non-essential navigation buttons are hidden to save screen space, and can optionally be displayed with the "Show more" button.
Some tables still need horizontal scrolling. This is intentionally done to display the information in a meaningful way.

In this conversion, I followed Google's recommendations for responsive design and verified the web site with Google's webmaster tools.
I make no effort to accommodate old browsers or unusual software/hardware platforms.

Site history

I started this web site in 1990, hosting it on a Windows PC under my desk in my university office. It is currently hosted by a US-based web provider and its contents are in accordance to and protected by US laws (in particular, by their strong protection of freedom of expression). I am physically resident in Sweden, which grants a similar freedom of expression.

This web site was hacked just once, on May 17, 2000 (when it was running under Microsoft IIS on another host). The home page was substituted with this. For a free, and very likely more reliable, multi-platform alternative to Microsoft Internet Information Services, see the Apache web server.

Over 10 years ago I stopped using my own web server, and since then I have been running this web site on servers provided by hosting companies in the United States.

Hardening against hacking

This web site contains only static HTML pages, so it is extremely unlikely that hackers will find anything to do here. There are no databases and no web CMS to break into, no web application to break, no user comments or bulletin board to harvest or troll, no way to upload anything through the web interface, and no server-side languages to exploit. Just plain old HTML, client-side Javascript, and one client-side Java applet.

All content creation, templating and styling is done offline at a remote location before uploading the HTML to the server. If a hacker should succeed in completely deleting this web site, I can simply upload an exact copy within minutes on this or another web server.


This site does not use cookies.

Ad blockers

This site does not require you to switch off your ad blocker. You are welcome to use it on this site, although it makes no difference because there are no ads on this site (with the possible exception of sponsored links on the Google search results page, which is generated by Google).

Links to other sites

In accordance with EU law, I can link to your (or any other) publicly accessible web site without asking your permission and regardless of whether the materials I am linking to are copyrighted. Cross-linking to images and other media on another site to make it appear as a part of the linking site is explicitly allowed by EU law, regardless of whether the link target is copyrighted. Many other countries or states have similar laws.

Distribution of page hits (whole site) during the last month.
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This site is ad-free. If you see any ads here, they are added by your ISP, or by spyware on your computer, or you are visiting this site through frames of another site.