Published online by Cambridge University Press: 12 March 2014
A Boolean algebra (henceforth abbreviated B.A.) is said to be recursive if B is a recursive subset of the natural numbers N and the operations ∧ (meet), ∨ (join), and ¬ (complement) are partial recursive. Let
denote the set of atoms of
and
denote the ideal generated by the atoms of
. Given recursive B.A.s
and
, we write
≈
if
is isomorphic to
and
≈r
if
is recursively isomorphic to
, i.e., if there is a partial recursive isomorphism from
onto
.
Recursive B.A.s have been studied by several authors including Ershov [2], Fiener [3], [4], Goncharov [5], [6], [7], LaRoche [8], Nurtazin [7], and the author [10], [11]. This paper continues a study of the recursion theoretic relationships among ,
, and the recursive isomorphism type of a recursive B.A.
we started in [11]. We refer the reader to [11] for any unexplained notation and definitions. In [11], we were mainly concerned with the possible recursion theoretic properties of the set of atoms in recursive B.A.s. We found that even if we insist that
be recursive, there is considerable freedom for the properties of
. For example, we showed that if
is a recursive B.A. such that
is recursive and
is infinite, then (i) there exists a recursive B.A.
such that
and both
and
are recursive and (ii) for any nonzero r.e. degree δ, there exist recursive B.A.s
,
, … such that for each i,
is of degree δ,
is recursive,
is immune if i is even and
is not immune if i is odd, and no two B.A.s in the sequence are recursively isomorphic.