This is the current version of a short book about atoms that I am writing. The book begins with a discussion of automata models for infinite alphabets. Then, inspired by these automata, the book develops the theory of orbit finite sets with atoms and computation on them. If you find mistakes in the current version, please put them here.

All versions:

• December 4, 2018
• November 30, 2018
• April 15, 2017