Karnaugh Maps / Tables
The Karnaugh map was invented in 1952 by Edward W. Veitch. It was further developed in 1953 by Maurice Karnaugh, a physicist at Bell Labs, to help simplify digital electronic circuits.
In a Karnaugh map the boolean variables are transferred (generally from a truth table) and ordered according to the principles of Gray code in which only one variable changes in between squares. Once the table is generated and the output possibilities are transcribed, the data is arranged into the largest even group possible and the minterm is generated through the axiom laws of boolean algebra. - Wikipedia
Karnaugh Map (also known as the Veitch Diagram) reduction was developed as a graphic method of minimizing Boolean function. The 4-variable Karnaugh Map reduction shown here applies to any size map.