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Maximal vector spaces under automorphisms of the lattice of recursively enumerable vector spaces

Published online by Cambridge University Press:  12 March 2014

Iraj Kalantari
Affiliation:
Cornell University, Ithaca. NY 14853
Allen Retzlaff
Affiliation:
Cornell University, Ithaca. NY 14853

Extract

The area of interest of this paper is recursively enumerable vector spaces; its origins lie in the works of Rabin [16], Dekker [4], [5], Crossley and Nerode [3], and Metakides and Nerode [14]. We concern ourselves here with questions about maximal vector spaces, a notion introduced by Metakides and Nerode in [14]. The domain of discourse is V a fully effective, countably infinite dimensional vector space over a recursive infinite field F.

By fully effective we mean that V, under a fixed Gödel numbering, has the following properties:

(i) The operations of vector addition and scalar multiplication on V are represented by recursive functions.

(ii) There is a uniform effective procedure which, given n vectors, determines whether or not they are linearly dependent (the procedure is called a dependence algorithm).

We denote the Gödel number of x by ⌈x⌉ By taking {εnn > 0} to be a fixed recursive basis for V, we may effectively represent elements of V in terms of this basis. Each element of V may be identified uniquely by a finitely-nonzero sequence from F Under this identification, εn corresponds to the sequence whose n th entry is 1 and all other entries are 0. A recursively enumerable (r.e.) space is a subspace of V which is an r.e. set of integers, ℒ(V) denotes the lattice of all r.e. spaces under the operations of intersection and weak sum. For V, W ∈ ℒ(V), let V mod W denote the quotient space. Metakides and Nerode define an r.e. space M to be maximal if V mod M is infinite dimensional and for all V ∈ ℒ(V), if VM then either V mod M or V mod V is finite dimensional. That is, M has a very simple lattice of r.e. superspaces.

Type
Research Article
Copyright
Copyright © Association for Symbolic Logic 1977

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