## New to the Gateway?

The Gateway to Logic is a collection of web-based logic programs offering a number of logical functions (e.g. truth tables, normal forms, proof checking, proof building). If you are a new user to the Gateway, consider starting with the simple truth-table calculator or with the Server-side functions.

On each category page, beneath the headline of the respective page, there
are two important links: **"Other programs"** and
**"Help"**. You can at any time return to this
overview page by selecting **"Other programs"**.
The link **"Help"** will open up a new page
(or browser tab) showing a detailed documentation of the respective
program category.

Operating the Logic server currently costs about 113.88€ per year (virtual server 85.07€, domain fee 28.80€); hence the Paypal donation link.

## Server side

The server side functions operate on formulae of classical two-valued propositional logic. They work with any browser. Although the server side offers a few graphical functions (e.g. displaying syntax trees), its strengths lie in the field of syntactic operations like optimization (where it offers e.g. a Quine-McCluskey reducer), normal forms and showing truth-tables.

## Proof Checker

The Proof Checker, umh, checks proofs submitted by the user - hence the name. It supports Lemmon's calculus only. As opposed to the Proof Builder, the Proof Checker requires the user to actually type in the proof she wants to check. For this reason, many people find the Proof Builder easier to use.

## Simple truth tables

The simple truth-table calculator calculates the tables directly in your browser, so the calculator is available offline, and the government won't ever find out what propositions you are working with (unless it hacks your computer). It is not intended as a ready-to-use product, but as a first test for the feasibility of migrating to more up-to-date web technology.

## Proof Builder

In the past, there were a number of Java applets allowing to interactively "build" proofs in miscellaneous logical calculi (Lemmon style, Fitch style, Hilbert style, Principia Mathematica and Peirce's Alpha Graphs). Java Applets have long been retired and no current browser will be able to run them (you might still use an old, Java-aware browser locked in a VM, though), but there is a downloadable standalone version of the Alpha Graph Proof Builder: Download the file Peirce.jar to your computer and open it e.g. by double-clicking (for this to work, you will need a working installation of Java which is available for free at https://www.java.com/download/).

## Author

The Gateway to Logic is © by Christian Gottschall. Any kind of feedback, problem report, or proposed improvement is welcome at any time.