ABSTRACT. It is shown that every finite lattice, and in fact every recursively presentable lattice, can be embedded in the r.e. tt-degrees by a map preserving least and greatest elements. The decidability of the I-quantifier theory of the Le. ttdegrees in the language with ~, v, /\, 0, and 1 is obtained as a corollary. tt-degrees and about questions relating to the decidability of the theory of the r.e. tt-degrees. They show there that every recursively presentable lattice can be embedded in the r.e. tt-degrees preserving least element. Using this, they show that the 3 theory of the r.e. tt-degrees in the language with ~ , V, 1\,0 is decidable, and ask whether the 3 theory is still decidable when 1 is added to the language. This decidability question can be answered by determining which finite lattices can be embedded in the r.e. tt-degrees preserving least and greatest elements. Jockusch and Mohrherr [3] have shown that the diamond lattice, the pentagon lattice, and the I-n-llattices can be embedded preserving least and greatest elements, but leave open the general question, and even such special cases as the three generator Boolean algebra. The embedding used in their proof requires that the lattice in question have the property that no element which is the inf of a pair of incomparable elements of the lattice can be joined up to the 1 of the lattice (except by 1 itself). We show here that all finite lattices, and in fact all recursively presentable lattices, can be embedded in the r.e. tt-degrees preserving least and greatest elements (provided the lattice has distinct least and greatest elements). Our proof for the general lattices combines a generalization of the coding method used by Jockusch and Mohrherr with the strategy for preserving nonzero infs used by Fejer and Shore.
Introduction. A setWe prove first, in §l, that every lattice with a finite representation (and distinct least and greatest elements) can be embedded, and then in §2 outline the modifications needed to embed a recursively presented (possibly infinite) lattice. As a