Math 5020 Spring 2017
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Course Information:
Syllabus
In this course we give a development of modern set theory.
We begin with a develop of the \(\mathsf{ZFC}\) axioms of set theory, and develop the basic
properties of models of set theory. We give a rigorous presentation of ordinals and cardinals,
and fundamental notions such as absoluteness and definability. We discuss independence and
the incompleteness theorem as it pertains to set theory. We discuss inner models such as
\(L\) and HOD, and show, for example, that GCH holds in \(L\). We develop forcing
and us it to get various consistency results as well as a tool for proving theorems.
We discuss combinatorial principles such as \(\diamond\) and MA. Other topics as time permits.
We will not follow a single text exclusively, but a good reference is Set Theory, an Introduction to
Independence Proofs
by K. Kunen. Another good reference is Set Theory by T. Jech. We will also
use class notes which I will post on the website.
Here are two notes to get started. I will be modifying these notes as the class progresses.
Axioms of set theory
Ordinals,
Ordinal arithmetic,
Cardinals,
Absoluteness
Forcing,
Independence of CH
HW #1.
1.) Exercise 21 in the notes: show that for all sets \( x_1,\dots,x_n\), the set
\(y= \{ x_1,\dots,x_n\} \) exists.
2.) Exercise 24 in the notes: show that for any relation \( R\) that
\( \text{dom}(R) \) and \( \text{ran}(R) \) are sets.
3.) Show that \( \mathsf{ZF} \vdash \neg \exists x \, \forall y\, (y \in x) \).
Follow the informal argument of Russell's paradox, but give the argument rigorously
from \( \mathsf{ZF} \).
4.) Exercise 6 from the ordinal notes.
HW #2. Due Thursday, March 1.
1.) Write out a formula in the language of set theory \( \varphi(x,y) \)
which holds in a model of ZF iff \( y\) is the transitive closure of \( x\).
Show that \( \mathsf{ZF} \vdash \forall x\ \exists y\ \varphi(x,y) \).
2.) Show that if \( \alpha, \beta\) are ordinals and each can be order-embedded into the
other, then \( \alpha =\beta\).
3.) View the exponential function \( f(n)=2^n\) as being defined by recursion:
\( f(0)=1\) and \( f(n+1)= 2\cdot f(n)\). Write a formula \( \varphi(m,n)\)
in the languge of set theory
which holds in a model of \( \mathsf{ZF} \)
iff \(m, n\) are integers and \( n=2^m\). You don't have to go down to the
level of a formal wff just using \( \epsilon\), but it should be clear that you could
continue to do so.
HW #3.
1.) Let \( \alpha= \omega^3\cdot 2 +\omega^2\cdot 5 +3\) and \( \beta= \omega^4\cdot 3 +\omega\cdot 6+7\).
Compute \( \alpha+\beta\), \( \beta+\alpha\), \( \alpha \cdot \beta\), and \( \alpha^\beta\).
2.) Let \( \kappa\) be a strong limit cardinal. Show that \( \text{cof}(\gimel(\kappa)) >\kappa\).
3.) Exercise 13 from the notes: Suppose \( \kappa\) is a singular limit cardinal. Suppose there is a
\( \lambda <\kappa\) such that \( \lambda^{\text{cof}(\kappa)} \geq \kappa\), and let \( \lambda\)
be the least such. Show that \( \text{cof}(\lambda) \leq \text{cof}(\kappa)\).
[hint: suppose \( \text{cof}(\kappa) < \text{cof}(\lambda)\), and show
that \( \lambda^{\text{cof}(\kappa)} <\kappa\). You will need to show that \( \text{sup} \{
\mu^{\text{cof}(\kappa)} \colon \mu <\lambda\} <\kappa \)]
HW #4.
1.) Exercise 1 of the forcing notes: show every generic \( G\) meets every predense
set and every maximal antichain.
2.) Exercise 3 of the forcing notes: show that \( p \Vdash \neg \neg \varphi\) iff \( p \Vdash
\varphi\).
3.) Exercise 2 of the continuum notes: show that \( \prod_{\alpha \in I} {\mathbb{R}}_{\text{std}}\)
is c.c.c.