Originally trained as an architect and engineer, Greek composer Iannis Xenakis has forged a distinctive musical style through the application of various branches of mathematics to his compositional process. Early in his career he focused on topics in probability. After his initial concentration on mathematical models of indeterminacy, he began to incorporate more deterministic methods of organization into his compositions, including set theory and group theory'. Herma is a composition for solo piano written in 1960-61. It is representative of the coexistence of determinacy and indeterminacy in the structure of his works, and thus serves as a good introduction to the music of this remarkable composer.