The abstract:

This paper presents μKanren, a minimalist language in the miniKanren family of relational (logic) programming languages. Its implementation comprises fewer than 40 lines of Scheme. We motivate the need for a minimalist miniKanren language, and iteratively develop a complete search strategy. Finally, we demonstrate that through sufcient user-level features one regains much of the expressiveness of other miniKanren languages. In our opinion its brevity and simple semantics make μKanren uniquely elegant.