News about the LeMoDa website

2026-05-30

★ New page on Cauchy-Schwarz inequality

I've added a new page on proving the Cauchy-Schwarz inequality using induction.

2026-05-28

★ New page on intersection of circles

I've added a new page on how to calculate the points of intersection of two circles.

2026-05-19

★ Errata page for an old book on topology

I added a page on errata for an old book on topology by Max Newman.

2026-05-16

★ More pictures on the submarine page

I added more pictures on /maths/submarine/.

★ Page on errata in Cajori book

I added a page on errata in a book on equations: /books/cajori-errata/.

2026-05-13

★ Trigonometry in one picture

A new page, maths/trig-picture/, has an SVG version of a picture that I found online.

2026-04-29

★ New page on an analytic geometry problem

/maths/complex-circles/ is an answer to a problem of analytic geometry in the complex plane.

★ Improvements to the "old mathematics books" page

I did some work on improving the book on out-of-copyright mathematics books maths/old-books/.

2026-04-28

★ New pages on a physics problem and two maths problems

I added a new page physics/vulcan/ about a physics problem from French's Newtonian Mechanics book, /maths/n-factorial/ about the divergence of the nth root of n factorial, /maths/submarine/, a problem about differential equations.

2026-04-27

★ Work on trigonometry page

I did some work on the neglected page on trigonometry /maths/trig/. I don't really remember making this page, but the date on it says 2021. I found some errors which I've corrected, and also some useless outputs which I've removed. I also added some mnemonics. I will try to add some graphics as well.

★ Tetrahedron page

I've added a new page on the geometry of the tetrahedron, maths/tetrahedron/.

2026-04-25

★ Links checked

All the external links from lemoda.net to other websites were checked for validity, mostly automatically and in a few cases by hand.

2026-04-22

★ New page on equilateral triangles in the complex plane

I made a new page maths/complex-equilateral/.

★ New page on printf-like-functions in Go

A new page go/printf-like-function/. I keep forgetting how to do this, then going to web pages which give an incorrect answer to the problem, so I've put this here.

2026-04-19

★ New page on the orthocentre of a triangle

New page maths/orthocentre/.

2026-04-18

★ New page on the circumcentre of a triangle

New page maths/triangle-bisectors/.

2026-04-15

★ Convert numbers to Chinese and European languages

The European language versions of tools/chinese-numbers/ now try to work out whether the user is using a "." as a separator for thousands rather than as a decimal point.

2026-04-11 08:29:03

★ Various links updated

Various outgoing links were either changed for correct versions or for archive.org versions for pages which have disappeared.

The pages affected are:

2026-04-08

★ New page on converting Go comments

I added a script perl/gocomment/ which I thought might be useful for somebody.

2026-04-07

★ Removed bad robots and referrer spammer pages

The list of bad robots and referrer spammers both dated from 2011 and so are probably no longer relevant, so I've removed them both.

★ Overhaul of Chinese number page

I've added French, German and Thai to the Chinese number page tools/chinese-numbers/. I also did some internal work on some silly bugs and other things which needed fixing in the page. For example, an empty string no longer turns into "zero", and badly formed requests are rejected. There are also a few more user error messages, based on a review of the user inputs over the last year or two.

2026-04-04

★ Link fixes

I changed to an archive.org link at electricity/three-phase-motor-questions/, updated a link at perl/template-encoding/ to the new URL and changed a link to the FreeBSD handbook at assembly/freebsd-hello-world/.

★ Removed "Common tasks with flex"

I've removed the page "Common tasks with flex" since Flex (the parser software, not the Adobe animation) has changed since I wrote it, about fifteen years ago, and the links from the page were broken.

★ qrpng.org links from kanji.sljfaq.org, nxmnpg.lemoda.net

I've updated the websites kanji.sljfaq.org and nxmnpg.lemoda.net so that the QR code images which appear on those pages are now pointing to tools/qrpng/.

2026-04-03

★ New page on constructing a pentagon with ruler and compass

There is a new page on constructing a pentagon using a ruler and a compass, maths/pentagon/.

2026-04-02

★ Links to the Flex manual sections on Bison and yyextra removed

The page c/reentrant-parser had links to the online manual for Flex about Bison and yyextra, but the online manual has gone so I removed those links.

2026-04-01

★ Top level category "handwritten" removed

I removed the top level category "handwritten" since it is now empty after the kana page was removed.

2026-03-27

★ Handwritten kana page removed

The server for the experimental handwritten kana input was turned off some time ago, and today I removed the pages themselves, as it wasn't working any more.

2026-03-25

★ Old categories removed

I removed three categories, convert-moji, life-in-japan, and streetview, because all of these had no pages under them due to the removals on 23 March 2026.

2026-03-23

★ Link checking

Two links to grokbase.com were replaced with archive.org links. A link to linuxsoftware.co.nz was replaced with an archive.org link.

Various http: links were replaced with https: ones.

The site floodit.appspot.com has disappeared, and although the page is archived at archive.org, nothing seems to appear on the page, so the link from /javascript/flood-it/ has been removed.

Various links to the old golang.org site were changed to the new go.dev site.

A link to nihongo.monash.edu was changed to edrdg.org.

A link to redhat.com on windows/windows2unix/windows2unix.html was replaced by an archive.org one. Other links were replaced by https. One faulty link, to serverfault.com, was replaced by a corrected link.

A link to the keystroke help page for the Lynx web browser on lynx/exit-lynx-without-message/ was removed since it had never been archived.

A link to the Moby Project at gutenberg.org was removed from /english/resources/ because it could not be found there any more.

★ Large shoes page removed

The page on buying large shoes in Japan has been removed, since the information given was for a shop which has now closed down.

★ Make romaji songs removed

I removed the song lyrics pages from this website some time ago, so this page about making romanised song lyrics isn't relevant any more.

★ Old maths book gone

One of the books on maths/old-books/, "A course of modern analysis" by Whittaker, was removed from archive.org, so that link was removed from here.

2026-03-03

★ Link checking

Links to some defunct web pages were substituted with links to archive.org.

Some of the links to sites which are now https changed from http to https, such as gutenberg.org on books/gutenberg-recommends/.

golang.org changed to pkg.go.dev on go/perl-go/.

ietf.org changed to rfc-editor.org on cgi/simple-guide/.

An unarchived link on word/perl-get-paragraphs/ was removed. This was going to a spam site unfortunately so was better deleted.

Some links to codepad.org removed.

Two links to oshiete.goo.ne.jp changed to archive.org links.

★ Removed an old page

Removed perl/cpan-projects. This page concerned an old project called the CPAN pull request challenge and had not been updated in ten years.