This page list all events and seminars that take place in the department this week. Please use the form below to choose a different week or date range.

## BGU Probability and Ergodic Theory (PET) seminar

### On pointwise periodicity and expansiveness

Mar 20, 11:00-12:00, 2018, 201

#### Speaker

Tom Meyerovitch (BGU)

#### Abstract

Following Kaul, a discrete (topological) group G of transformations of set X is pointwise periodic if the stabilizer of every point is of finite index (co-compact) in G. Equivalently, all G-orbits are finite (compact). Generalizing a result of Montgomery, Kaul showed in the early 70’s that a pointwise periodic transformation group is always compact when the group acts (faithfully) on a connected manifold without boundary. I will discuss implications of expansiveness and pointwise periodicity of certain groups and semigroups of transformations. In particular I’ll state implications for cellular automata and for planner tilings. Based on joint work with Ville Salo.

## Colloquium

### Lipschitz geometry of singularities

Mar 20, 14:30-15:30, 2018, Math -101

#### Speaker

Lev Birbrair (Universidade Federal do Ceara)

#### Abstract

“Singularities’’ are points in a geometric region which are different from most nearby points in the region. Their study uses many mathematical tools. One of these tools is what is called bi-Lipschitz geometry’’, which permits alteration of a geometric object by applying limited local stretching and shrinking. For example, a bi-Lipschitz change to the geometry of a knife preserves the sharpness of the knife, but may turn a dinner knife into a butter knife.

Applying bi-Lipschitz geometry to singularities retains their basic structure while making them much easier to classify and therefore easier to work with. Despite this, it is only fairly recently that bi-Lipschitz geometry has been applied much in singularity theory, but its use has grown rapidly in the last decade as an increasing number of researchers are starting to work with it. It is a powerful tool for a variety of mathematical problems.

## Research Features

### תורת המודלים: קשרים מפתיעים בין גיאומטריות קומבינטוריות למבנים אלגברים קלאסיים

Mar 20, 16:15-18:00, 2018, -101

אסף חסון

## אשנב למתמטיקה

### מזעריות-סדר: גן העדן בו אין אינטגרלים, כל הפונקציות גזירות, וגבולות תמיד קיימים

Mar 20, 18:15-19:45, 2018, אולם 101-

אסף חסון

#### The Big Rock Candy Mountains

One evening as the sun went down And the jungle fires were burning, Down the track came a hobo hiking, And he said, “Boys, I’m not turning I’m headed for a land that’s far away Besides the crystal fountains So come with me, we’ll go and see The Big Rock Candy Mountains

In the Big Rock Candy Mountains, There’s a land that’s fair and bright, Where the handouts grow on bushes And you sleep out every night. Where the boxcars all are empty And the sun shines every day And the birds and the bees And the cigarette trees The lemonade springs Where the bluebird sings In the Big Rock Candy Mountains.

In the Big Rock Candy Mountains All the cops have wooden legs And the bulldogs all have rubber teeth And the hens lay soft-boiled eggs The farmers’ trees are full of fruit And the barns are full of hay Oh I’m bound to go Where there ain’t no snow Where the rain don’t fall The winds don’t blow In the Big Rock Candy Mountains.

In the Big Rock Candy Mountains You never change your socks And the little streams of alcohol Come trickling down the rocks The brakemen have to tip their hats And the railway bulls are blind There’s a lake of stew And of whiskey too You can paddle all around it In a big canoe In the Big Rock Candy Mountains

In the Big Rock Candy Mountains, The jails are made of tin. And you can walk right out again, As soon as you are in. There ain’t no short-handled shovels, No axes, saws nor picks, I’m bound to stay Where you sleep all day, Where they hung the jerk That invented work In the Big Rock Candy Mountains.

## Algebraic Geometry and Number Theory

### The structure of flat modules and the module structure of flat algebras over commutative rings

Mar 21, 15:10-16:30, 2018, Math -101

#### Speaker

Leonid Positselski (University of Haifa)

#### Abstract

The Govorov-Lazard theorem describes flat modules over any associative ring as filtered direct limits of finitely generated free modules, but a more informative description may be desirable. I will explain how to obtain the flat modules over a Noetherian commutative ring which has either Krull dimension 1, or an arbitrary Krull dimension but countable spectrum, as the direct summands of transfinitely iterated extensions of localizations of the ring with respect to countable multiplicative subsets. An even more precise description, with localizations of the ring at its elements (= multiplicative subsets generated by one element), is obtained for the underlying modules of flat finitely presented commutative algebras over arbitrary commutative rings. I will start with a discussion of complete cotorsion pairs in module categories and proceed to formulate the above mentioned results and explain some of the ideas behind their proofs. This talk is based on the speaker’s joint work with Alexander Slavik.