3 papers
math.LO2004
Ladder gaps over stationary sets
Uri Abraham, Saharon Shelah
For a stationary set S subseteq omega_1 and a ladder system C over S, a new type of gaps called C-Hausdorff is introduced and investigated. We describe a forcing model of ZFC in wh…
math.LO2001
Coding with ladders a well-ordering of the reals
Uri Abraham, Saharon Shelah
Any model of ZFC + GCH has a generic extension (made with a poset of size aleph_2) in which the following hold: MA + 2^{aleph_0}= aleph_2+ there exists a Delta^2_1-well ordering of…
math.LO1998
A Delta^2_2 well-order of the reals and incompactness of L(Q^{MM})
Uri Abraham, Saharon Shelah
A forcing poset of size 2^{2^{aleph_1}} which adds no new reals is described and shown to provide a Delta^2_2 definable well-order of the reals (in fact, any given relation of the…