Abstract.
We prove the following theorem: For a partially ordered set Q such that every countable subset of Q has a strict upper bound, there is a forcing notion satisfying the countable chain condition such that, in the forcing extension, there is a basis of the null ideal of the real line which is order-isomorphic to Q with respect to set-inclusion. This is a variation of Hechler’s classical result in the theory of forcing. The corresponding theorem for the meager ideal was established by Bartoszyński and Kada.
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Research supported by NSERC. The first author thanks F.D. Tall and the Department of Mathematics at the University of Toronto for their hospitality during the academic year 2003/2004 when the present paper was completed.
The second author was supported by Grant-in-Aid for Young Scientists (B) 14740058, MEXT.
Mathematics Subject Classification (2000): 03E35, 03E17
Revised version: 16 February 2004
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Burke, M., Kada, M. Hechler’s theorem for the null ideal. Arch. Math. Logic 43, 703–722 (2004). https://doi.org/10.1007/s00153-004-0224-4
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DOI: https://doi.org/10.1007/s00153-004-0224-4