September 2017
Probably due to a compiler bug triggered by a recent change (no joking!), the server-side functions of the Gateway to Logic stopped computing conjunctive normal forms (CNFs). Many thanks to ElĂ­as F. Combarro who noticed, and made me aware of the problem.
March 2017
Dr. Klaus Dethloff, admired teacher and scholar, dies on March, 15th (obituary [German]).
starting a transition to HTML5
April, 10th 2012
It became necessary to change a hard disk of the Logic Server. I found this a welcome opportunity for updating the Linux distribution used. As a side-effect of the configuration works done, there is now an HTTPS server running, too.
February, 25 2011
[Icon]Truth Tables for Android - due to the much more powerful Android platform, this version is highly improved over its recent counterparts, e.g. supporting, besides classical logic, a number of non-classic, multi-valued logical systems.
Nothing happened in 2009. Maybe more things happened in German?
May, 5th 2008
The Server-side functions of the Gateway to Logic now provide an optimizer suitable for dealing with canonical normal forms. In general, this leads to shorter CNFs than in the past.
January, 9th 2008
After more than eight years of service, the venerable Celeron 366 hardware of the Logic Server was retired. It has been replaced by an up-to-date new computing device that covers less space than a paperback, is much more environmentally friendly by consuming only 0,1-10 Watt per hour (depending on system load), and, most important, whose exterior is of truly splendid yellow colour.
Nothing happened in 2007. Maybe more things happened in German?
December, 28th 2006
The Axiomatic Proof Builder that is part of the Gateway to Logic now supports defining connectives (see also the Principia Mathematica-style version of the Axiomatic Proof Builder).
August, 12nd 2006
There is an axiomatic (Hilbert-style) proof builder for propositional logic.
January, 11th 2006
Today n such that n is the number of bugs of the Peirce Alpha Graph Proof Builder has been decreased by one. From now on, it is also possible directly to apply the rule of Iteration to a negation, meaning that it is no longer impossible to derive the valid argument (P)|-(P)(P).
January, 8th 2006
Thanks to a hint from Jon Merzel, two bugs in the Lemmon-style Proof Builder have been eliminated: vI now quotes the right line number (i.e. without incrementing it by 1), and vE more carefully checks the dependencies within the sub-derivations.
September, 1st 2005
There are ongoing attempts to restructure the web pages at the Logic Server. This may lead to temporary inconsistencies, missing pages, dangling links and so on. If you experience any problem, please let me know (
August, 14th 2005
Now the Gateway to Logic supports the logical system of Charles Sanders Peirce, too: The Alpha Graph Proof Builder has gone online today.
March, 28th 2005
Both the Lemmon-style Proof Builder and the Fitch-style Proof Builder offer the following two features:
  • Copy & paste: If your Java subsystem is configured to allow applets clipboard access, you may copy the proof to the clipboard
  • Print view: Even if your Java subsystem does not allow clipboard access, you may copy the proof from the new "Print view" window by the copy & paste feature of your operating system. If your browser is capable of printing a window's content, you may as well directly print the proof.
It was Ole Koksvik who proposed this useful feature.
September, 3rd 2002
The server side of the Gateway to Logic now supports conjunctive normal forms (CNF and CCNF).
August, 10th 2002
I have added another server side function to the Gateway to Logic. To a given proposition, the new function shows the Begriffsschrift notation (i.e. the notation introduced by Gottlob Frege in his 1879 "Begriffsschrift").
August, 3rd 2002
A new function has been added to the Gateway to Logic. The new server side function graphically shows the alpha graph to a given proposition. Alpha graphs are a notation devised by the American philosopher Charles Sanders Peirce.
August, 31st 1999
In addition to the Lemmon style proof builder, the Gateway to Logic now contains a Fitch style proof builder restricted to propositional logic.
August, 31st 1999
Due to many requests from users of the Gateway to Logic, I have committed myself to the following statement of year 2000 compliance.
April, 12th 1999
The server side of the Gateway to Logic now offers graphical expression trees without requiring Java support on the client side.
March, 6th 1999
The Quine-McCluskey optimizer of my Gateway to Logic is now available in two versions, one of them accepting partial truth tables, the other accepting plain propositions of propositional logic.
March, 5th 1999
The Logic Server has entered into diplomatic relations with the Planet of Sheep!
February, 25th 1999
The Proof Builder of the Gateway to Logic now supports lemmas and their application. There will be some documentation in the near future.
February, 1st 1999
My Gateway to Logic now also offers Quine-McCluskey optimization.
January, 26th 1999
The Computer Service Department of the Humanities which hosted my web pages has been finally closed. For this reason the old URLs "" and "" are not valid any longer. Please be so kind to update your bookmarks and/or referring pages and to inform the webmistress(es) and/or webmaster(s) responsible for the referring pages and/or the persons responsible for informing the webmistress(es) and/or webmaster(s) about changes to addresses to which their pages refer about this change.
November, 20th 1998
The new beta version of my program checking for propositional intuitionistic validity is now part of the server side of my Gateway to Logic. An improved algorithm covers the whole of intuitionistic logic. (The old algorithm was a bit faster, but sometimes covered not all possibilities.)
November, 9th 1998
The Gateway to Logic was awarded Links2Go Key Resource - Logic Topic
June, 13th 1998
From now on, you can reach me via ICQ, number 14014915.
May, 28th 1998
The server side of my Gateway to Logic now offers a new function to check propositions for their intuitionistic validity.
January, 29th 1998
I have set up a questionaire to get some ideas on who is using my Gateway to Logic and what problems they are experiencing. Please feel free to fill out the form - you would be the fourteenth one to do so.