Six Ukrainian articles on semigroup theory by A. K. Sushkevich

This is an English translation of six articles, originally written in Ukrainian, by the semigroup theorist Anton Kazimirovich Sushkevich (1889-1961). The articles date between 1935 and 1939, and were all written in Kharkiv. A preface is also included, giving a summary of the articles and the purpose of the translation.