The goal of this tutorial is to give a quick introduction on how to use the relational algebra calculator and its concepts. It assumes that you already know the relational algebra or are learning it from other sources.
There is no real standard for the relational algebra like there is for SQL. So every book or teacher might have its slightly different interpretation and notation.
The goal of this program was to support the most commonly used "mathematical" notation used by Database Systems The Complete Book 2nd Edition by Hector Garcia-Molina, Jeff Ullman, and Jennifer Widom, Datenbanksysteme: Eine Einführung by Alfons Kemper and André Eickler and Wikipedia - Relational Algebra and others.
See this paper for details and please cite it if you're using RelaX:
Johannes Kessler, Michael Tschuggnall and Günther Specht: RelaX: A Webbased Execution and Learning Tool for Relational Algebra, In: Proceedings of the Datenbanksysteme für Business, Technologie und Web (BTW), 18. Fachtagung des GI-Fachbereichs 'Datenbanken und Informationssysteme', March 2019, Rostock, Germany, 2019