Christian Wolff presented Cage with a copy of a book which had a symbol system used to identify randomness in ordered events.
He was still using magic square-like charts to introduce chance into composition, when, in early 1951, Christian Wolff presented Cage with a copy of the I Ching (Wolff's father published a translation of the book at around the same time). This Chinese classic text is a symbol system used to identify order in chance events. 
