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On finite lattices of degrees of constructibility

Published online by Cambridge University Press:  12 March 2014

Zofia Adamowicz*
Affiliation:
Instytut Matematyczny, Pan, Poland

Extract

We shall prove the following theorem:

Theorem. For any finite lattice there is a model of ZF in which the partial ordering of the degrees of constructibility is isomorphic with the given lattice.

Let M be a standard countable model of ZF satisfying V = L. Let K be the given finite lattice. We shall extend M by forcing.

The paper is divided into two parts. The first part concerns the definition of the set of forcing conditions and some properties of this set expressible without the use of generic filters.

We define first a representation of a lattice and then the set of conditions. In Lemmas 1, 2 we show that there are some canonical isomorphisms between some conditions and that a single condition has some canonical automorphisms.

In Lemma 3 and Definition 7 we show some methods of defining conditions. We shall use those methods in the second part to define certain conditions with special properties.

Lemma 4 gives a connection between the sets P and Pk (see Definitions 4 and 5). It is next employed in the second part in Lemma 10 in an essential way.

Indeed, Lemma 10 is necessary for Lemma 13, which is the crucial point of the whole construction. Lemma 5 is also employed in Lemma 13 (exactly in its Corollary).

The second part of the paper is devoted to the examination of the structure of degrees of constructibility in a generic model. First, we show that degrees of some “sections” of a generic real (Definition 9) form a lattice isomorphic with K. Secondly, we show that there are no other degrees in the generic model; this is the most difficult property to obtain by forcing. We prove, in two stages, that it holds in our generic models. We first show, by using special properties of the forcing conditions, that sets of ordinal numbers have no other degrees. Then we show that the degrees of sets of ordinals already determine the degrees of other sets.

Type
Research Article
Copyright
Copyright © Association for Symbolic Logic 1977

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References

REFERENCES

[1]Adamowicz, Zofia, On finite lattices of degrees of conslructibility of reals, this Journal, vol. 41 (1976), pp. 313322.Google Scholar
[2]Grigorieff, Serge, Combinatorics on ideals and forcing, Annals of Mathematical Logic, vol. 3 (1971), pp. 363394.CrossRefGoogle Scholar
[3]Lachlan, A. H. and Lebeuf, R., Countable initial segments of the degrees of unsolvability, this Journal, vol. 41 (1976), pp. 313323.Google Scholar
[4]Lerman, M., Initial segment of the degrees of unsolvability, Annals of Mathematics, vol. 93 (1971), pp. 365389.CrossRefGoogle Scholar