By Joan Bagaria, Stevo Todorcevic

This quantity has its origins within the examine Programme on Set thought and its purposes that came about on the Centre de Recerca Matemática (CRM) Barcelona from September 2003 to July 2004. It includes elements. the 1st comprises survey papers on a number of the mainstream components of set theory, and the second one includes unique study papers.

The survey papers conceal topics as Omega-logic, purposes of set conception to lattice idea and Boolean algebras, real-valued measurable cardinals, complexity of units and family in continuum conception, susceptible subsystems of axiomatic set idea, definable models of huge cardinals, and choice concept for open covers of topological areas. As for the examine papers, they vary from themes equivalent to the variety of near-coherence sessions of ultrafilters, the consistency power of bounded forcing axioms, some functions of morasses, subgroups of Abelian Polish groups, the consistency energy of mutual stationarity, and new axioms of set theory.

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**Example text**

Since each P(x) is contractible there is an equivalence P(x) ≃ unit for each x ∶ A. By the univalence axiom we get a path P(x) ↝ unit. Since we have a path P ↝ U, there is a path between the types ( ∏(x ∶ A), P(x)) ↝ ( ∏(x ∶ A), U(x)) so we only have to verify that ∏(x ∶ A), U(x), which is equal to A → unit, is contractible. 6. We finish this section with two new applications of the univalence axiom. The first is an observation of Bas Spitters, which he shared with the author at the Fourth Workshop on Formal Topology in Ljubljana in 2012.

Using the function extensionality principle, it suffices to show that ∏(x ∶ unit), ϕ( f (tt))(x) ↝ f (x). To show that such a section exists, we use the induction principle for unit once more: note that ϕ( f (tt))(tt) = f (tt). 6. For every space A there is an equivalence A ≃ (unit → A). 7 (Correspondence theorem for empty). Suppose P is a dependent type over the empty type empty. Then we have an equivalence unit ≃ ∏(x ∶ empty), P(x). 45 P ROOF. Note that it suffices to show that ∏(x ∶ empty), P(x) is contractible.

Proj1 ⟨ f (x),⟨x,id f (x) ⟩⟩ = λ x. f (x) = f , which finishes the proof. The second application of the univalence axiom asserts that the notions of function and graph coincide. We have chosen to state the theorem in its non-dependent form, but the proof of the dependent version of the assertion goes along the same lines. 10. e. there is an equivalence ( ∑(R ∶ A → B → Type) ∏(a ∶ A), isContr( ∑(b ∶ B), R(a,b))) ≃ A → B. P ROOF. For any function f ∶ A → B there is the relation R f ∶ A → B → Type given by R f (a,b) ∶= f (a) ↝ b.