Published online by Cambridge University Press: 12 March 2014
Metakides and Nerode in [2] suggested the study of what they termed the lattice of recursively enumerable substructures of a recursively presented model. For example, Metakides and Nerode in [3] introduced the lattice of of recusively enumerable subspaces, , of a recursively presented vector space V∞. The similarities and differences between
and ℰ, the lattice of recursively enumerable subsets of the natural numbers N as defined in [9], have been studied by Metakides and Nerode, Kalantari, Remmel, Retzlaff, and Shore. In [6], we studied some similarities and differences between ℰ and the lattice of recursively enumerable sub-algebras of a weakly recursively presented Boolean algebra and this paper continues that study. A weakly recursively presented Boolean algebra (W.R.P.B.A.),
, consists of a recursive subset of N, ∣
∣, called the field of
, and operations
(meet),
(join), and
(complement) which are partial recursive and under which
becomes a Boolean algebra. We shall write
and
for the zero and unit of
. If S is a subset of
, we let (S)* denote the subalgebra generated by S. Given sub-algebras B and C of
, we let B + C denote (B ⋃ C)*. A subalgebra B of
is recursively enumerable (recursive) if {x ∈ ∣
∣ x ∈ B} is a recursively enumerable (recursive) subset of ∣
∣. The set of all recursively enumerable subalgebras of
,
, forms a lattice under the operations of intersection and sum (+).