
doi: 10.2307/421005
The purpose of this communication is to survey a theory of liftings, as developed in author's thesis ([8]). The first result in this area was Shelah's construction of a model of set theory in which every automorphism ofP(ℕ)/ Fin, where Fin is the ideal of finite sets, istrivial, or inother words, it is induced by a function mapping integers into integers ([33]). (It is a classical result of W. Rudin [31] that under the Continuum Hypothesis there are automorphisms other than trivial ones.) Soon afterwards, Velickovic ([47]), was able to extract from Shelah's argument the fact that every automorphism ofP(ℕ)/ Fin with a Baire-measurable lifting has to be trivial. This, for instance, implies that in Solovay's model ([36]) all automorphisms are trivial. Later on, an axiomatic approach was adopted and Shelah's conclusion was drawn first from the Proper Forcing Axiom (PFA) ([34]) and then from the milder Open Coloring Axiom (OCA) and Martin's Axiom (MA) ([48], see §5 for definitions). Both shifts from the quotientP(ℕ)/ Fin to quotients over more general idealsP(ℕ)/Iand from automorphisms to arbitrary ho-momorphisms were made by Just in a series of papers ([14]-[17]), motivated by some problems in algebra ([7, pp. 38–39], [43, I.12.11], [45, Q48]) and topology ([46, p. 537]).
Other set-theoretic hypotheses and axioms, Open Coloring Axiom, Martin's Axiom, analytic P-ideals, Continuum hypothesis and Martin's axiom, Baire-measurable lifting, Other combinatorial set theory
Other set-theoretic hypotheses and axioms, Open Coloring Axiom, Martin's Axiom, analytic P-ideals, Continuum hypothesis and Martin's axiom, Baire-measurable lifting, Other combinatorial set theory
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