부산대학교 도서관

A language $L$ is called prefix-convex if the fact that $w,u\in L$ with $u$ a prefix of $w$ implies that $v\in L$ for any prefix $v$ of $w$ such that $u$ is a prefix of $v$. In the work under review, the authors introduce in a quite similar manner suffix-convex, bifix-convex, factor-convex, subword-convex languages, and their closed and free counterparts, and then study the relationships among these languages. Finally they extend the above notions to arbitrary binary relations between words over a given alphabet, and discuss the closure properties of such languages.