The (rnrs lists (6)) library provides a small number of useful procedures operating on lists, including several procedures from R5RS. The goal of the library is to provide only procedures likely to be useful for many programs. Consequently, the selection represented by (rnrs lists (6)) is less exhaustive than the widely implemented SRFI 1 . Several changes were made with respect to the corresponding procedures SRFI 1 to simplify the specification, and to establish uniform naming conventions.
Although they are ordinarily used as predicates, memp, member, memv, and memq, do not have question marks in their names because they return useful values rather than just #t or #f.