And we have a video from the last year’s ISI conference. Where you can see how the shape is created:

Both of my kids are also GeoGebra fans, but they are too young to really understand the difference between proof and verification yet. A proof is a theoretical confirmation that a statement (for example, “the bisector lines of a triangle are concurrent”) is always true. A verification is usually an experiment, that the statement is indeed true, by choosing a large set of examples.

GeoGebra is not the first software which provides proving. The first pieces of software were written back in the 1980’s. But oddly enough, many of the first scientific papers were also written by researchers of University of Linz, lead by Professor Bruno Buchberger, founder of the Gröbner basis theory.

Now GeoGebra has several built-in methods to decide if a statement is true in general or not, and one of the used methods is based on Gröbner bases. To avoid heavy computations on a single workstation, we can outsource them to another software, namely Singular, which runs as a web service remotely. On the other hand, we also use a sophisticated method to avoid symbolic computations completely. Professor Tomas Recio, a Spanish expert of algebraic geometry, developed this idea, and Simon Weitzhofer (mentioned in my first post) implemented it in Java recently.

Luckily enough, even other colleagues joined us from different countries. Professor Francisco Botana, a pioneer in open source based mathematics, also from Spain, and Professor Predrag Janicic from University of Belgrade, lead developer of GCLC, offered their help in extending GeoGebra with state-of-the-art methods to provide fast computations. Also Ivan Petrovic, a PhD student of Predrag, works on the open sourced, Java based OpenGeoProver, to enhance it to be an optional prover engine for GeoGebra. We also have a Google Summer of Code 2012 student, Damien Desfontaines from Paris, France, in our group, who helps Ivan to implement the area method, to extend the set of applicable statements for proving. One day maybe we will have readable proofs as well, since the fast algorithms usually don’t give acceptable output for a human. But currently we are really satisfied with some yes/no/unknown result, which should also be used in both experimenting and teaching mathematics.

The basics are working already good, fast and intuitively enough. See this table for an overview: Botana’s method is the Singular based Gröbner basis calculation, pure symbolic method is just dealing with parametric polynomials in Java internally, the OpenGeoProver backend is not listed yet. (The numbers mean milliseconds.) One can also try Recio’s method (and as fallback, the pure symbolic method) in the web version of GeoGebra, or wait for the desktop version (4.1.81.0 should be stable enough, but it is not released yet at the moment), or just watch this YouTube video. For those who are interested in the details, the documentation of the Prove and ProveDetails commands will also help.