andrzej roslanowski and saharon shelah- iteration of lambda-complete forcing notions not collapsing...

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  (   6   5   5   )  r  e  v   i  s   i  o  n  :   2   0   0   1    1   1    1   2  m  o   d   i   f   i  e   d  :   2   0   0   1    1   1    1   2 ITERATION OF λ-COMPLETE FOR CING NOTIONS NOT COLLAPSING λ + . ANDRZEJ ROS LANOWSKI AND SAHARON SHELAH Abstract. We look for a parallel to the notion of “proper forcing” among λ-complete forcing notions not collapsing λ + . We sugges t such a denit ion and pro ve that it is prese rve d by suitabl e itera tions . 0. Introduction This work follows [Sh 587] and [Sh 667] (and see history there), but we do not rely on those papers. Our goal in this and the previous papers is to dev elop a theory parall el to “propernes s in CS iterations” for iterations with larger supports. In [Sh 587], [Sh 667] we have presented parallels to [Sh 64] and [Sh:98], whereas here we try to hav e parallels to [Sh 100], [Sh:b, Ch.III], [Sh:b, Ch.V,§5-§7] and hopefully [Sh:f, Ch.VI], [Sh:f, Ch.XVIII]. It seems too much to hope for a notion fully parallel to “proper” among λ-complete forcing notions as even for “ λ + -c.c. λ-complete there are prob- lems. We should also remember about ZFC limitations for possible iteration theore ms. F or example, if in the denition of the forcing notion Q in Sec- tion 3 we demand h  p e δ h δ , then the proof fails. This ma y se em a drawback, but one should look at [Sh:f, AP, p.985, 3.6(2) and p.990, 3.9]. By it, if S = S λ + λ , and (A δ ,h δ are as in 3.4 and) we ask a success on a club, then for some h δ : δ S λ + λ we fai l. Now, if we all ow only h δ : A δ −→ 2 and we ask for “success of the uniformization” on an end segment of A δ (for all such A δ : δ S λ + λ ), then we also fail as we may code colourings with values in λ. In the rst section we formulate our denitions (including prop erness over λ, see 1.3) . We believe that our main Deni tio n 1.3 is quite reasonable and appli cable. One may also dene a version of it where the diamon d is “sprea d out”. The second secti on is dev oted to the proof of the preserv ation theorem, and the next one gives three (relatively easy) examples of forcing not ions tting our sc heme. We conclude the paper wit h the discussi on of applications and variants. Key words and phrases. Forcing, iterations, not collapsing cardinals, proper. Both authors would like to thank the United States-Israel Binational Science Founda- tion for partial support. This publication has number 655 in Shelah’s list. 1

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Page 1: Andrzej Roslanowski and Saharon Shelah- Iteration of lambda-Complete Forcing Notions Not Collapsing lambda^+

8/3/2019 Andrzej Roslanowski and Saharon Shelah- Iteration of lambda-Complete Forcing Notions Not Collapsing lambda^+

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