This is a lecture on the properties of open sets in finite-dimensional Euclidean space by Dr Joel Feinstein from his second-year module on Mathematical Analysis. This material is suitable for those who already know the definitions of open set and of the interior of a set in finite-dimensional Euclidean space.

In this session Dr Feinstein shows that finite unions and intersections of open sets are open, and then discusses infinite unions and intersections. It turns out that infinite unions of open sets are still open, but that infinite intersections of open sets need not be open any more.

See also Dr Feinstein's blog, Explaining Mathematics, http//explainingmaths.wordpress.com/

Properties of open sets - Dr Joel Feinstein

A selection of recordings suitable for third-year mathematics undergraduate students at university.

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This is a lecture from Dr Feinstein's 4th-year module G14FUN Functional Analysis.

See also Dr Feinstein's blog at http://explainingmaths.wordpress.com/ and, in particular, the Functional Analysis screencasts blog page at http://wp.me/PosHB-8v

In this screencast, Dr Feinstein discusses two famous results concerning collections of bounded linear operators, one of which is a corollary of the other. Both of these results have been called the Banach-Steinhaus Theorem (by various authors). The stronger of these two results is the one which is also known as the Uniform Boundedness Principle.
This material is suitable for those with a good background knowledge of metric spaces and normed spaces. In particular, the student should know about bounded (continuous) linear operators between normed spaces, and the Baire Category Theorem for complete metric spaces.

The Uniform Boundedness Principle - Dr Joel Feinstein

This video is a combination of the three screencasts from Chapter 9 of the second year module G12MAN Mathematical Analysis, lectured by Dr J. Feinstein (Nottingham). See also Dr Feinstein's blog at http://explainingmaths.wordpress.com/ and, in particular, the associated blog post at http://wp.me/posHB-7j

The aim of this material is to introduce the student to two notions of convergence for sequences of real-valued functions. The notion of pointwise convergence is relatively straightforward, but the notion of uniform convergence is more subtle. Uniform convergence is explained in terms of closed function balls and Dr Feinstein's notion of sets absorbing sequences.

The differences between the two types of convergence are illustrated with several examples. Some standard facts are also discussed: a uniform limit of continuous functions must be continuous; a uniform limit of bounded functions must be bounded; a uniform limit of unbounded functions must be unbounded.

Target audience: Most of this material should be accessible to anyone who understands what a real-valued function is, and understands the notion of convergence of a sequence of real numbers. This should include most mathematics undergraduates by the end of their first year. An understanding of continuity and of boundedness for real-valued functions defined on various types of domain would help the student to understand the latter part of the material.

Uniform convergence and Pointwise convergence

This popular maths talk by Dr Joel Feinstein gives an introduction to various different kinds of infinity, both countable and uncountable. These concepts are illustrated in a somewhat informal way using the notion of Hilbert's infinite hotel. In this talk, the hotel manager tries to fit various infinite collections of guests into the hotel. The students should learn that many apparently different types of infinity are really the same size. However, there are genuinely "more" real numbers than there are positive integers, as is shown in the more challenging final section, using Cantor's diagonalization argument. This last part of the talk is relatively technical, and is probably best suited to first-year mathematics undergraduates, or advanced maths A level students. Others may find the technical details hard to follow, and should focus on the overview. Dr Joel Feinstein's blog is available at http://explainingmaths.wordpress.com/

Beyond Infinity? Dr Joel Feinstein

This is a lecture from Dr Feinstein's 4th-year module G14FUN Functional Analysis.

See also Dr Feinstein's blog at http://explainingmaths.wordpress.com/ and, in particular, the associated blog post at http://wp.me/posHB-7y In this screencast, Dr Feinstein proves the Baire Category Theorem for complete metric spaces - a countable intersection of dense, open subsets of a complete metric space must be dense.

This material is suitable for those with a knowledge of metric space topology and, in particular, dense subsets and complete metrics.

Properties of open sets - Dr Joel Feinstein

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