Embedding finite lattices into the ideals of computably enumerable turing degrees
William C. Calhoun, Manuel Lerman · Journal of Symbolic Logic · 2001
Abstract. We show that the lattice L20 is not embeddable into the lattice of ideals of computably enumerable Turing degrees (ℐ), We define a structure called a pseudolattice that generalizes the notion of a lattice, and show that there is a Π2 necessary and sufficient condition for embedding a finite pseudolattice into ℐ.