The following is taken from my book Quite by Chance - Wie durch Zufall:
During the 1980s I attended a number of courses in computer music and bought my first computer, an Atari. Compared with today's machines this was very large and very slow but in spite of this I was able to use it for computer music and a primitive music notation program which I developed myself and also simple programming with Basic.
I had had an enquiry from Dominik Blum for a piece for cello and piano and I wanted to realise this new piece with chance procedures. I decided that the piece would be a game of Snakes and Ladders. This children’s game uses a board with 100 numbers on it. Players roll dice to see how many steps they can make. If they’re lucky, they land on a ladder and can climb up to the number at the top of the ladder. If they’re unlucky they land on the head of a snake and must slither down to the number at the tail of the snake.
The piece therefore would be a contest between the pianist and the cellist. There would be a shake theme for the player preparing to roll the die, followed by a turn which contains n (die-no.) moves. At the end there could also be a snake or a ladder depending on where the turn ends.
First I had to invent the board and decide where the snakes and ladders would lie: The diagram below was the first sketch (red snakes and blue ladders). I later found there were a few too many and removed some.
This information was given to the computer, which was also taught to roll dice and record the results. I let it play the game a number of times and chose the most interesting looking game.
So as to increase the tension in the piece, I decided that after half way through, both players would be shaking and moving simulteniously.
Here then is the game I chose for the piece:
Pitches were organised by a 10-note tone row: Because of its symmetry it is only ever used in its 12 transpositions.
The rhythmic patterns below are used for all of the turns. No. 1 is the mirror form of no. 10, and no. 2 is the mirror form of no. 9, etc.
This preoccupation with mirror forms started in the mid 80s while setting Harlow texts where mirrors frequently appear as a figure examines himself. I was fascinated by how such reflexions in music in contrast to parallels in the visual arts are not always obvious—which is good! Snakes and Ladders also included important elements of music theatre:
Throughout the score the players are instructed to show the emotions of the character they are playing; if he seems to be winning he is jubilant and the opponent is angry and vice versa. In the last two pages of the score (below) the cellist wins and is “ebullient”, the pianist on the other hand is “incensed”, closes the piano and leaves, while the cellist is so pleased with himself he starts playing a Bach solo cello-suite. The pianist notices this, returns, and angrily plays: B A C H (B A C B♮)