The LYON-program is Richard Lang’s sixth World Microcomputer Chess Championship success for Mephisto. Mephisto Lyon won the 10th WMCCC held in Lyon, France with commanding 6.5 points in 7 games, finishing one point ahead of second placed Echecs 1.9 and third placed Gideon.
The 16 Bit LYON program has 128 KB Rom and 512 KB RAM. The opening library consists of more than 100,000 half moves in 13,000 variations.
The program was improved tactically compared to its predecessor Portorose. These improvements were made by changing its selective behavior. Compared to its predecessor the LYON program selectively choses to search less moves, but searches the chosen moves on average 4 half moves deeper. The selection algorithm was also modified which allows the program to find the best moves very early in its search. The use of singular extensions were also introduced for the first time in a Mephisto computer. This allowed the program to search deeper into a tactical search line.
The program was sold in three versions: Motorola 68000, 68020 and 68030 microprocessors. This version is the Motorola 68000 16 Bit version. The playing strength is approximately ELO 2330 USCF.