Allotropy (1970) is the third piece for piano by Yori-Aki Matsudaira after Instruction (1961), inspired by the so-called John Cage Shock, and Figures for piano (1959, withdrawn), commissioned by NHK. Chopin’s ‘Raindrop’ (Prelude op. 28, no. 15), cited suddenly at the end of the piece, sounds so peculiar that it is seen as one of the most prominent examples of citation in the works of Matsudaira. As this implies, repetitive sounds are a salient feature of this work (‘allotropy’ means different structural modifications of an element). The piece consists of eight sections: the first presents series of repetitive sounds, the second combinations of repetition and clusters, etc. Then, repetitions in a pointillistic style are combined with the pianist’s voice such as ‘ta’ and ‘pa’, followed by violent repetitions of clusters with scream, quiet and pointillistic repetitions, the recapitulation of all the elements presented before, and finally the ‘Raindrop’. In the coda, the pianist claps his hands near the strings of the piano. This coda was cut in the recording by the dedicatee Aki Takahashi, which was an advice of Roger Reynolds, as Matsudaira says. Allotropy was premiered by Aki Takahashi on 1 December 1970 at the small hall of Tokyo Bunka Kaikan. The score was published by Suvini Zerboni.