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| Content Provider | Springer Nature Link |
|---|---|
| Author | Dimitrov, R. D. Harizav, V. |
| Copyright Year | 2016 |
| Abstract | Let V ∞ be a standard computable infinite-dimensional vector space over the field of rationals. The lattice $$ \mathfrak{L} $$ (V ∞ ) of computably enumerable vector subspaces of V ∞ and its quotient lattice modulo finite dimension, $$ \mathfrak{L} $$ *(V ∞ ), have been studied extensively. At the same time, many important questions still remain open. In 1998, R. Downey and J. Remmel posed the question of finding meaningful orbits in $$ \mathfrak{L} $$ *(V ∞ ) [4, Question 5.8]. This question is important and difficult and its answer depends on significant progress in the structure theory for the lattice $$ \mathfrak{L} $$ *(V ∞ ), and also on a better understanding of its automorphisms. Here we give a necessary and sufficient condition for quasimaximal (hence maximal) vector spaces with extendable bases to be in the same orbit of $$ \mathfrak{L} $$ *(V ∞ ). More specifically, we consider two vector spaces, V 1 and V 2 , which are spanned by two quasimaximal subsets of, possibly different, computable bases of V ∞ . We give a necessary and sufficient condition for the principal filters determined by V 1 and V 2 in $$ \mathfrak{L} $$ *(V ∞ ) to be isomorphic. We also specify a necessary and sufficient condition for the existence of an automorphism Φ of $$ \mathfrak{L} $$ *(V ∞ ) such that Φ maps the equivalence class of V 1 to the equivalence class of V 2 . Our results are expressed using m-degrees of relevant sets of vectors. This study parallels the study of orbits of quasimaximal sets in the lattice ε of computably enumerable sets, as well as in its quotient lattice modulo finite sets, ε * , carried out by R. Soare in [13]. However, our conclusions and proof machinery are quite different from Soare’s. In particular, we establish that the structure of the principal filter determined by a quasimaximal vector space in $$ \mathfrak{L} $$ *(V ∞ ) is generally much more complicated than the one of a principal filter determined by a quasimaximal set in ε* . We also state that, unlike in ε* , having isomorphic principal filters in $$ \mathfrak{L} $$ *(V ∞ ) is merely a necessary condition for the equivalence classes of two quasimaximal vector spaces to be in the same orbit of $$ \mathfrak{L} $$ *(V ∞ ). |
| Starting Page | 440 |
| Ending Page | 477 |
| Page Count | 38 |
| File Format | |
| ISSN | 00025232 |
| Journal | Algebra and Logic |
| Volume Number | 54 |
| Issue Number | 6 |
| e-ISSN | 15738302 |
| Language | English |
| Publisher | Springer US |
| Publisher Date | 2016-03-11 |
| Publisher Place | New York |
| Access Restriction | One Nation One Subscription (ONOS) |
| Subject Keyword | infinite-dimensional vector space over field of rationals quasimaximal set equivalence classes principal filter orbit lattice Algebra Mathematical Logic and Foundations |
| Content Type | Text |
| Resource Type | Article |
| Subject | Logic Algebra and Number Theory Analysis |
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