Jean-Benoît Bost told me a beautiful proof of the main ingredient in the proof of Galois correspondence, which had been published by Lagrange in his 1772 “Réflexions sur la résolution des résolutions algébriques”, almost 60 years before Galois. (See Section 4 of that paper, I think; it is often difficult to recognize our modern mathematics in the language of these old masters.)

In modernized notations, Lagrange considers the following situation. He is given a polynomial equation $ T^n + a_{n-1} T^{n-1}+\cdots + a_0 = 0$, with roots $x_1,\dots,x_n$, and two “rational functions” of its roots $f(x_1,\dots,x_n)$ and $\phi(x_1,\dots,x_n)$. (This means that $f$ and $\phi$ are the evaluation at the $n$-tuple $(x_1,\dots,x_n)$ of two rational functions in $n$ variables.) Lagrange says that $f$ and $\phi$ are similar (“semblables”) if every permutation of the roots which leaves $f(x_1,\dots,x_n)$ unchanged leaves $\phi(x_1,\dots,x_n)$ unchanged as well (and conversely). He then proves that $\phi(x_1,\dots,x_n)$ is a rational function of $a_0,\dots,a_{n-1}$ and $f(x_1,\dots,x_n)$.

Let us restate this in a more modern language. Let $K\to L$ be a finite Galois extension of fields, in the sense that $K= L^{G}$, where $G=\mathop{\rm Aut}_K(L)$. Let $a, b\in L$ and let us assume that every element $g\in G$ which fixes $a$ fixes $b$ as well; then Lagrange proves that $b\in K(a)$.

Translated in our language, his proof could be as follows. In formula, the assumption is that $g\cdot a=a$ implies $g\cdot b=b$; consequently, there exists a unique *function* $\phi\colon G\cdot a\to G\cdot b$ which is $G$-equivariant and maps $a$ to $b$. Let $d=\mathop{\rm Card}(G\cdot a)$ and let us consider Lagrange's interpolation polynomial —the unique polynomial $P\in L[T]$ of degree $d$ such that $P(x)=\phi(x)$ for every $x\in G\cdot a$. If $h\in G$, the polynomial $P^h$ obtained by applying $h$ to the coefficients of $P$ has degree $d$ and coincides with $\phi$; consequently, $P^h=P$. By the initial assumption, $P$ belongs to $K[T]$ and $b=P(a)$, hence $b\in K(a)$, as claimed.

Combined with the primitive element theorem, this allows to give another short, and fairly elementary, presentation of the Galois correspondence.

# Freedom Math Dance

A blog about math (mainly), computer tricks (sometimes) and jazz music.

## Monday, March 23, 2015

## Saturday, February 28, 2015

### Galois Theory, Geck's style

This note aims at popularizing a short note of Meinolf Geck, “On the characterization of Galois extensions”, Amer. Math. Monthly 121 (2014), no. 7, 637–639 (Article, Math Reviews, arXiv), that proposes a radical shortcut to the treatment of Galois theory at an elementary level. The proof of the pudding is in the eating, so let's see how it works. The novelty lies in theorem 2, but I give the full story so as to be sure that I do not hide something under the rug.

Let $K\to L$ be a field extension and let $P\in K[T]$. We say that $P$ is split in $L$ if it is a product of linear factors in $L[T]$. We say that $P$ is separable if all of its roots (in some extension where it is split) have multiplicity $1$. We say that $K\to L$ is a splitting extension of $P$ if $P$ is split in $L$ and if $L$ is the subextension of $K$ generated by the roots of $P$ in $L$. Finally, we let $\mathop{\rm Aut}_K(L)$ be the set of $K$-linear automorphisms of $L$; it is a group under composition.

If these equivalent conditions hold, we say that the finite extension $K\to L$ is Galois.

**Proposition 1.***Let $K\to L$ be a field extension. Then $L$ is not the union of finitely many subfields $M$ such that $K\to M\subsetneq L$.*Proof. It splits into two parts, according whether $K$ is finite or infinite.

Assume that $K$ is finite and let $q=\mathop{\rm Card}( K)$. Then $L$ is finite as well, and let $n=[L:K]$ so that $\mathop{\rm Card}(L)=q^n$. If $M$ is a subextension of $L$, then $\mathop{\rm Card}( L)=q^m$, for some integer $m$ dividing $n$; moreover, $x^{q^m}=x$ for every $x\in L$. Then the union of all strict sub-extensions of $L$ has cardinality at most $\sum_{m=1}^{n-1} q^m =\frac{q^n-q}{q-1}<q^n$.

It remains to treat the case where $K$ is infinite; then the proposition follows from the fact that a finite union of strict subspace of a $K$-vector space $E$ is not equal to $E$. Let indeed $(E_i)_{1\leq i\leq n}$ be a family of strict subspaces of $E$ and let us prove by induction on $n$ that $E\neq \bigcup_{i=1}^n E_i$. The cases $n\leq1$ are obvious. By induction we know that for every $j\in\{1,\dots,n\}$, the union $\bigcup_{i\neq j}E_i$ is distinct from $E$, hence select an element $x\in E$ such that $x\not\in E_2\cup \dots\cup E_n$. The desired result follows if, by chance, $x\not\in E_1$. Otherwise, choose $y\in E\setminus E_1$. For $s\neq t\in K$, and $i\in\{2,\dots,n\}$, observe that $y+sx$ and $y+tx$ cannot both belong to $E_i$, for this would imply that $(s-t)x\in E_i$, hence $x\in E_i$ since $s\neq t$. Consequently, there are at most $n-1$ elements $s\in K$ such that $y+sx\in \bigcup_{i=2}^nE_i$. Since $K$ is infinite, there exists $s\in K$ such that $y+sx\not\in\bigcup_{i=2}^n E_i$. Then $y+sx\not\in E_1$, neither, since $x\in E_1$ and $y\in E_1$. This proves that $E\neq \bigcup_{i=1}^nE_i$.

Let $K\to L$ be a field extension and let $P\in K[T]$. We say that $P$ is split in $L$ if it is a product of linear factors in $L[T]$. We say that $P$ is separable if all of its roots (in some extension where it is split) have multiplicity $1$. We say that $K\to L$ is a splitting extension of $P$ if $P$ is split in $L$ and if $L$ is the subextension of $K$ generated by the roots of $P$ in $L$. Finally, we let $\mathop{\rm Aut}_K(L)$ be the set of $K$-linear automorphisms of $L$; it is a group under composition.

**Theorem 2.***Let $K\to L$ be a finite extension of fields and let $G=\mathop{\rm Aut}_K(L)$. Then $\mathop{\rm Card}( G)\leq [L:K]$. Moreover, the following conditions are equivalent:*

*One has $\mathop{\rm Card}( G)=[L:K]$;*- There exists an irreducible separable polynomial $P\in K[T]$ such that $\deg(P)=[L:K]$ and which is split in $L$;
- The extension $K\to L$ is a splitting extension of a separable polynomial in $K[T]$;
- One has $K=L^G$.

**Remark 3.**In the conditions of (2), let us fix a root $z\in L$ of $P$. One has $L=K(z)$. Moreover, the map $f\mapsto f(z)$ is a bijection from $\mathop{\rm Aut}_K(L)$ to the set of roots of $P$ in $L$.Proof of Theorem 2.

(a) Let us prove that $\mathop{\rm Card} (G)\leq [L:K]$. Let $m\in\mathbf N$ be such that $m\leq \mathop{\rm Card}( G)$ and let $\sigma_1,\dots,\sigma_m$ be distinct elements of $G$. For $1\leq i<j\leq m$, let $M_{i,j}$ be the subfield of $L$ consisting of all $x\in L$ such that $\sigma_i(x)=\sigma_j(x)$. It is a strict subextension of $L$ because $\sigma_i\neq\sigma_j$. Consequently, $L$ is not the union of the subfields $M_{i,j}$ and there exists an element $z\in L$ such that $\sigma_i(z)\neq \sigma_j(z)$ for all $i\neq j$. Let $P$ be the minimal polynomial of $z$. Then the set $\{\sigma_1(z),\dots,\sigma_m(z)\}$ consists of distinct roots of $P$, hence $\deg(P)\geq m$. In particular, $m\leq [L:K]$. Since this holds for every $m\leq \mathop{\rm Card}( G)$, this shows that $\mathop{\rm Card}( G)\leq [L:K]$.

(b) If one has $\mathop{\rm Card}( G)=[L:K]$, then taking $m=\mathop{\rm Card}( G)$, we get an irreducible polynomial $P\in K[T]$ of degree $m$, with $m$ distinct roots in $L$. Necessarily, $P$ is separable and split in $L$. This gives (1)$\Rightarrow$(2).

The implication (2)$\Rightarrow$(3) is obvious.

(1)$\Rightarrow$(4). Let $M=L^G$. One has $\mathop{\rm Aut}_K(L)=\mathop{\rm Aut}_M(L)=G$. Consequently, $\mathop{\rm Card}(G)\leq [L:M]$. Since $\mathop{\rm Card}( G)=[L:K]=[L:M][M:K]$, this forces $M=K$.

(4)$\Rightarrow$(3). There exists a $G$-invariant subset $A$ of $L$ such that $L=K(A)$. Then $P=\prod_{a\in A}(T-a)$ is split in $L$, and is $G$-invariant. Consequently, $P\in K[T]$. By construction, $P$ is separable and $L$ is a splitting extension of $P$.

(3)$\Rightarrow$(1). Let $M$ be a subextension of $L$ and let $f\colon M\to L$ be a $K$-morphism. Let $a\in A$ and let $Q_a$ be the minimal polynomial of $a$ over $M$. The association $g\mapsto g(a)$ defines a bijection between the set of extensions of $f$ to $M(a)$ and the set of roots of $Q_a$ in $L$. Since $P(a)=0$, the polynomial $Q_a$ divides $P$, hence it is separable and split in $L$. Consequently, $f$ has exactly $\deg(Q_a)=[M(a):M]$ extensions to $M(a)$.

By a straightforward induction on $\mathop{\rm Card}(B)$, for every subset $B$ of $A$, the set of $K$-morphisms from $K(B)$ to $L$ has cardinality $[K(B):K]$. When $B=A$, every such morphism is surjective, hence $\mathop{\rm Card}(\mathop{\rm Aut}_K(L))=[L:K]$.

If these equivalent conditions hold, we say that the finite extension $K\to L$ is Galois.

**Corollary 4.***Let $K\to L$ be a finite Galois extension. The maps $H\to L^H$ and $M\to \mathop{\rm Aut}_M(L)$ are bijections, inverse one of the other, between subgroups of $\mathop{\rm Aut}_K(L)$ and subextensions $K\to M\subset L$.*Proof. a) For every subextension $K\to M\subset L$, the extension $M\subset L$ is Galois. In particular, $M=L^{\mathop{\rm Aut}_M(L)}$ and $\mathop{\rm Aut}_M(L)=[L:M]$.

b) Let $H\subset\mathop{\rm Aut}_K(L)$ and let $M=L^H$. Then $M\to L$ is a Galois extension and $[L:M]=\mathop{\rm Aut}_M(L)$; moreover, one has $H\subset\mathop{\rm Aut}_M(L)$ by construction. Let us prove that $H=\mathop{\rm Aut}_M(L)$. Let $z\in L$ be any element whose minimal polynomial $P_z$ over $M$ is split and separable in $L$. One has $\mathop{\rm Card}(\mathop{\rm Aut}_M(L))=\deg(P_z)$. On the other hand, the polynomial $Q_z=\prod_{\sigma\in H}(T-\sigma(z))\in L[T]$ divides $P_z$ and is $H$-invariant, hence it belongs to $L^H[T]=M[T]$. This implies that $P_z=Q_z$, hence $\mathop{\rm Card}(H)=\deg(P_z)=\mathop{\rm Card}(\mathop{\rm Aut}_M(L))$. Consequently, $H=\mathop{\rm Aut}_M(L)$.

**Corollary 5.***Let $K\to L$ be a Galois extension and let $K\to M\to L$ be an intermediate extension. The extension $M\to L$ is Galois too. Moreover, the following assertions are equivalent:*

*The extension $K\to M$ is Galois;*- $\mathop{\rm Aut}_M(L)$ is a normal subgroup of $\mathop{\rm Aut}_K(L)$;
- For every $\sigma\in\mathop{\rm Aut}_K(L)$, one has $\sigma(M)\subset M$.

Proof. (a) Let $P\in K[T]$ be a separable polynomial of which $K\to L$ is a splitting field. Then $M\to L$ is a splitting extension of $P$, hence $M\to L$ is Galois.

(b) (1)$\Rightarrow$(2): Let $\sigma\in \mathop{\rm Aut}_K(L)$. Let $z$ be any element of $M$ and let $P\in K[T]$ be its minimal polynomial. One has $P(\sigma(z))=\sigma(P(z))=0$, hence $\sigma(z)$ is a root of $P$; in particular, $\sigma(z)\in M$. Consequently, the restriction of $\sigma$ to $M$ is a $K$-morphism from $M$ to itself; it is necessarily a $K$-automorphism. We thus have defined a map from $\mathop{\rm Aut}_K(L)$ to $\mathop{\rm Aut}_K(M)$; this map is a morphism of groups. Its kernel is $\mathop{\rm Aut}_M(L)$, so that this group is normal in $\mathop{\rm Aut}_K(L)$.

(2)$\Rightarrow$(3): Let $\sigma\in\mathop{\rm Aut}_K(L)$ and let $H=\sigma\mathop{\rm Aut}_M(L)\sigma^{-1}$. By construction, one has $\sigma(M)\subset L^G$. On the other hand, the hypothesis that $\mathop{\rm Aut}_M(L)$ is normal in $\mathop{\rm Aut}_K(L)$ implies that $G=\mathop{\rm Aut}_M(L)$, so that $L^G=M$. We thus have proved that $\sigma(M)\subset M$.

(3)$\Rightarrow$(1): Let $A$ be a finite subset of $M$ such that $M=K(A)$ and let $B$ be its orbit under $\mathop{\rm Aut}_K(L)$. The polynomial $\prod_{b\in B}(T-b)$ is separable and invariant under $\mathop{\rm Aut}_K(L)$, hence belongs to $K[T]$. By assumption, one has $B\subset M$. This implies that $K\to M$ is Galois.

**Remark 6.**Let $L$ be a field, let $G$ be a finite group of automorphisms of $L$ and let $K=L^G$. Every element $a$ of $L$ is algebraic and separable over $K$; inded, $a$ is a root of the separable polynomial $\prod_{b\in G\cdot a}(T-b)=0$, which is $G$-invariant hence belongs to $K[T]$. There exists a finite extension $M$ of $K$, contained in $L$, such that $G\cdot M=M$ and such that the map $\mathop{\rm Aut}_K(L)\to \mathop{\rm Aut}_K(M)$ is injective. Then $K\to M$ is Galois, and $G=\mathop{\rm Aut}_K(M)$. Indeed, one has $G\subset\mathop{\rm Aut}_K(M)$, hence $K\subset M^{\mathop{\rm Aut}_K(M)}\subset M^G\subset L^G=K$. This implies that $K\to M$ is Galois and the Galois correspondence then implies $G=\mathop{\rm Aut}_K(M)$. The argument applies to every finite extension of $K$ which contains $M$. Consequently, they all have degree $\mathop{\rm Card}(G)$; necessarily, $L=M$.**Remark 7 (editions).**Matt Baker points out that the actual novelty of the treatment lies in theorem 2, the rest is standard. Also, remark 6 has been edited following an observation of Christian Naumovic that it is not a priori obvious that the extension $K\to L$ is finite.## Monday, January 26, 2015

### Vijay Iyer and Wadada Leo Smith at The Stone

I just had the chance to attend two sets with Vijay Iyer and Wadada Leo Smith tonight! That happened at The Stone, a small music room in NYC owned by John Zorn that features avant-garde jazz music (but not only).

The first set was a plain duet of these two artists. The Stone was packed and we had to sit on the floor. After 10 quite boring minutes during which Vijay played electronics only, he took on the piano and music emerged. Although Vijay had sheets of music prepared, this set sounded very free, especially concerning Wadada Leo Smith's playing—it seems he used all what a trumpet allows to create sound. However, the atmosphere was peaceful. For those who know some of Wadada Leo Smith's music, this was closer to Kulture Jazz than to Ten Freedom Summers which I had discussed on this blog last year

For the second set, came along Reggie Workman at the bass, Nitin Mitta on the tablas, and Patricia Franceschy on vibes. This made the music sound quite differently. The musicians had decided of a few melodic lines and ostinatos, and grooved on that. The tablas gave a wonderful color to the music, similar as the one on Tirtha (with Prasanna on the guitar, and Nitin Mitta on the tablas). The vibes also gave a good touch. It seems that there are nice vibes players in free jazz nowadays; I'm thinking for example of Jason Adasiewicz who plays in Nicole Mitchelle's Ice Crystals group.

It was my first night in New York City since 2 years. I am happy to have had the opportunity to hear these great artists. Tomorrow night, if the announced snow storm permits, I'll go listen to Ari Hoenig at the Smalls!

The first set was a plain duet of these two artists. The Stone was packed and we had to sit on the floor. After 10 quite boring minutes during which Vijay played electronics only, he took on the piano and music emerged. Although Vijay had sheets of music prepared, this set sounded very free, especially concerning Wadada Leo Smith's playing—it seems he used all what a trumpet allows to create sound. However, the atmosphere was peaceful. For those who know some of Wadada Leo Smith's music, this was closer to Kulture Jazz than to Ten Freedom Summers which I had discussed on this blog last year

For the second set, came along Reggie Workman at the bass, Nitin Mitta on the tablas, and Patricia Franceschy on vibes. This made the music sound quite differently. The musicians had decided of a few melodic lines and ostinatos, and grooved on that. The tablas gave a wonderful color to the music, similar as the one on Tirtha (with Prasanna on the guitar, and Nitin Mitta on the tablas). The vibes also gave a good touch. It seems that there are nice vibes players in free jazz nowadays; I'm thinking for example of Jason Adasiewicz who plays in Nicole Mitchelle's Ice Crystals group.

It was my first night in New York City since 2 years. I am happy to have had the opportunity to hear these great artists. Tomorrow night, if the announced snow storm permits, I'll go listen to Ari Hoenig at the Smalls!

## Wednesday, October 1, 2014

### Book review: Contemplative Practices in Higher Education

*Contemplative Practices in Higher Education*, by Daniel P. Barbezat and Mirabai Bush.

Jossey-Bass, 2014.

[Center for Contemplative Mind in Society] [Library of Congress] [Amazon] [Fnac] [Barnes&Noble]

“Contemplative practices in higher education”? what the f...? Does this means that we should have to have our students meditate instead of practicing mathematics by doing more and more exercises? Again, what the f... ? And is it really appropriate, in our universities (which, in France, are mostly

*laïques et républicaines*) to experiment such practices?

The subtitle of the book under review should perhaps reassure us:

*Powerful methods to transform teaching and learning*. Indeed, as its authors explain to us in the very first lines of its preface, contemplative practices always has a well established place in the intellectual inquiry, a place which goes well beyond their vital role in all the major religions and spiritual traditions. The authors acknowledge many objectives to these practices, pointing out 4 of them whose importance can difficultly be denied:

- Development of attention and focus;
- Deeper understanding of the content of the course;
- Compassion, relation with self; deepening of the moral and spiritual component of education;
- Development of personality, and of creativity.

Daniel Barbezat, a professor in economics at Amherst, explains for example how these methods allowed him to solve the following contradiction: how is it possible that his field (economics) pretends studying the mechanisms of decision that are supposed to lead people to well-being, without every considering the nature of well-being? He proposed to his class various alternatives, of the following kind:

- The class is divided in ten groups of three people; the member of one group receive $1000 each, the other nothing
- Everybody receives $200

David Haskell, who teaches environmental sciences and biology, adapted the reading method of monks (as he says,

*lectio*without too much

*divina*) to have his class study problems of hunger and development. He asked his students to alternate between periods of quiet rest (say one minute) and the reading of one or two sentences of the text (each one reads by turns) and to brief commentaries by the students, etc. Other teachers propose the students to behold some text, or some graphic representation, and then to comment it. Examples are given of the probability distribution of the hydrogen bromide atom, according to its energy levels, or to two charts of industrial production (in absolute vs relative value). The authors claim that such exercises deepen the relation with self, with the studied document, and with other materials of the course.

Mathematics are absent from this book. In a blog post hosted by the American mathematical society, Luke Wolcott evokes this possibility, but acknowledges that he did not go further than personal meditation. In fact, I could not find other explicit examples in various sources, even none in the archives of the Center for contemplative mind in society that the authors of this book lead. However, it seems to me that some practical exercises organised by a teacher such as Adrien Guinemer in his middle/high school classes go in that direction (notably, the study of sections of cubes, cones, cylinder made from plasticine).

There are at least two methods that I find interesting and that could easily be implemented in our classes:

- Meditation exercises at the beginning of the class — first have everybody focus his attention on its breath during five minutes, and then report it on the subject of the class.
- Introspection techniques to fight failure anxiety — the student is asked to solve an exercise while writing on his sheet everything that comes to his mind, whatever relation it has with the exercise.

The first part of the book proposes a theoretical and practical background that is necessary to appreciate the variety of these methods, as well as some issues that need to be avoided. Three of them seem particularly crucial to me, all of them requiring from the teacher a quite deep personal involvement in these contemplative practices:

- Assign to the contemplative exercises a clear pedagogical goal, whose impact can be evaluated;
- Disjoint the practice of these exercises from the cultural and religious backgrounds in which they were first devised;
- Be able of managing students who would not be at ease, or even would reject, such practices.

So let us try, and see.

## Saturday, May 31, 2014

### The evolution of higher education

After a few months of silence, a short blog post to indicate a few web links that I found interesting, rising concern about the evolution of higher education.

In February 2014, Counterpunch published a series of remarks by Noam Chomsky under the title

More recently (May 2014), the New York Times published an editorial,

In fact, I had been made aware of the problem by a few posts from the blog The Homeless Adjunct, notably this post from 2012 that clearly explains

In February 2014, Counterpunch published a series of remarks by Noam Chomsky under the title

*On Academic Labor*. (I found it first on Alternet, under the alternate title*How America's Great University System Is Getting Destroyed*.)*Fat-Cat Administrators at the Top 25*, where they quote a report from the Institute for Policy Studies indicating that "*student debt and low-wage faculty labor are rising faster at state universities with the highest-paid presidents*."In fact, I had been made aware of the problem by a few posts from the blog The Homeless Adjunct, notably this post from 2012 that clearly explains

*how the American university system was killed in five easy steps*:- Defund the university system;
- Deprofessionalize and impoverish the professors;
- Install a managerial/administrative class who take over governance of the university;
- Move in corporate culture and corporate money;
- Destroy the students.

- Decisive progress towards defunding was made in 2009 by the Sarkozy-Pécresse LRU-law. While the acronym stands for Liberty and Responsability of Universities, this law has been infamously referred to Autonomy of Universities. The French public universities are now allocated a global budget by the State, which they are now supposed to manage as they wish, except that the allocated budget is insufficient, and that they have almost no control of whatever. Many universities are on the edge of defaulting. So what we have under the eyes is nothing but a defunding of the system disguised as a change of allocation model.
- The number of permanent positions is sharply decreasing. Of course, the age-pyramid of the present professors is also a cause for this evolution, since almost all baby-boomers have now retire. But the decrease is not at all the same in all fields—for example, this year, there were many more open positions in applied mathematics than in pure mathematics. Probably, when it comes about cutting positions, the "applied"-color makes it nicer for university boards. Probably too, applied mathematicians have been better at explaining their rôle in society.
- Meanwhile, the administration is getting fatter. To manage the global budget, it has been necessary to hire full-time "managers". And to be able to attract them, it seems that their pay has nothing to do with the usual range among French public servants. At the same time, a new law reorganizes the higher-education system by forcing universities (as well as our innumerous engineering schools) to regroup themselves. This will create enormous beasts that will look like the Lernean Hydra. For example, the Paris-Saclay University regroups 22 higher education schools, among which 2 universities and 10 "grandes écoles"; it will host around 50.000 students and more than 10.000 professors and researchers! No doubt that it will require a heavy bureaucracy to manage this high number of people. And since we're split in many institutions, it will be hard to have the voice of academic freedom be listened to.

## Friday, February 14, 2014

### A map of the universe

If you'd be asked to tell what a

Here theories have esoteric nicknames, such as ACF, ACVF, SCF$_p^n$, or ``universal graph omitting a bowtie'' (an homage to Tom S. ? :-)), and properties have even more esoteric nicknames — NIP, o-minimal, NSOP$_{n+1}$, or superstable. To make it something more than an enjoyable

By the way, this is also a beautiful illustration of the power of HTML5.

*map of the universe*looks like, I'm pretty sure you'd imagine something on a dark background, with many dots representing planets, and shaded areas corresponding to galaxies. That map of the universe, drawn by Gabriel Conant, a graduate student at Berkeley, is of more or less like that. Except that dots are mathematical theories, and galaxies correspond to some stability properties defined in model theory.Here theories have esoteric nicknames, such as ACF, ACVF, SCF$_p^n$, or ``universal graph omitting a bowtie'' (an homage to Tom S. ? :-)), and properties have even more esoteric nicknames — NIP, o-minimal, NSOP$_{n+1}$, or superstable. To make it something more than an enjoyable

*invitation au voyage*, Gabriel indicated important specific examples, with their definitions and references.By the way, this is also a beautiful illustration of the power of HTML5.

## Saturday, February 1, 2014

### Wadada Leo Smith: Ten Freedom Summers

Last Saturday (January 25th), I attended a concert by trumpetist Wadada Leo Smith in Vitry/Seine, within the Sons d'hiver festival, which serves as a pretext for this blog entry.

I had been introduced to Wadada Leo Smith's music thanks to France Musique program

In

For

Then, although some parts of the concert seemed to be improvised, it all looked as if they played the music as it is written on a score. This was the more surprising for the drummer who, most always in jazz music, is left to imagining by himself how he should bring his playing to the music being created. (When drummers have scores, that's rarely drum scores, but more often that of the bass player, or simply the main theme with the chords changes.)

Even Pheeroan akLaff was obviously playing the drums as written on the score, but the compositions gave him a quite interesting role in the development of the music. Wadada Leo Smith had written long solos for the drums which began or ended the pieces. In fact, since the group that night had no bass player, but a cellist who played with the bow — anyway, Lindberg mostly plays with the bow on the CD too — the other musicians are not given the explicit harmonic/rhythmic pattern that a “walking bass” can impose on the music, so there's probably no point for the drummer to play a definite swing rhythm, which akLaff did not do.

And within Wadada Leo Smith's mostly meditative music, that was akLaff's playing — sometimes forceful, or with traces of military marches — that reminded us that Freedom is a fight.

An everyday-fight.

The first part featured the Anti Pop Consortium's machine-player HPrizm, accompanied by improvisers David Virelles (piano), Steve Lehman (saxophone) and Wadada Leo Smith (trumpet), as well by Emanuuel Pidre (visuals). I found this part a bit bland. HPrizm's music lacked inspiration, rhythm, and although the improvisers are remarkable musicians, it was probably difficult for them to build on a lame material. Steve Lehman saved most of it, I think, because his playing is very lyrical, and quite dense, so that he could made the music.

The second part was Wadada Leo Smith's

The second part was Wadada Leo Smith's

*Ten Freedom Summers —*well, only a part of it, although they played for almost two hours.*Ten Freedom Summers*is the title of a monumental series of compositions by Wadada Leo Smith: 19 pieces, lasting for 4 hours and a half, depicting those moments of American history where African american people fought for Freedom. The first piece, “Dred Scott, 1857” recalls the story of Dred Scott, a slave who filed a suit at the Supreme Court to be able to buy his freedom, and lost, when the Supreme court ruled (1857) that people of African origin, whether slave or free, were not citizens of the United States —anyway, Scott had been freed the very same year by his new owner. The second piece is about the Montgomery bus boycott initiated by Rosa Parks in 1944. Two pieces are also devoted to the US presidents John F. Kennedy and Lyndon Johnson, celebrating the New Frontier, and the Civil Rights act of 1964.I had been introduced to Wadada Leo Smith's music thanks to France Musique program

*Open Jazz*, when Alex Dutilh aired the piece “Kulture of Jazz”, from the*Kulture Jazz*CD. Most of the pieces of that disc are evocations of jazz through some prominent figures of jazz (Louis Armstrong, Billie Holiday, John Coltrane, Albert Ayler), African literature (Ayl Kwel Armah), or his personal life (Sarah Brown-Smith-Wallace). The “K” in the title, which reminds me of the Klan, already emphasized the fact that jazz is an African-american music of emancipation. That is the music that black people played, but didn't have the right to listen to.In

*Kulture Jazz*, Wadada Leo Smith is the only credited musician. He mostly plays the trumpet, an instrument that truly belongs to jazz music (although it is slightly less heared these days), but he also sings, plays percussions, as well as koto, a rarely heard instrument in this context!For

*Ten Freedom Summers,*he combines a jazz quartet (trumpet, bass, drums and piano) and the Southwest Chamber Ensemble, a 9-musician strings combo. The combo that was initially announced for the concert was Smith's Golden quartet (with Anthony Davis, piano; John Lindberg, bass; Pheeroan akLaff, drums), except that the bassist had broken his wrist and could not play. He was thus replaced by Ashley Waters (from the Southwest Chamber Ensemble) on cello. Consequently, but that's probably one of the miracles allowed for by improvised music, the concert sounded pretty much like the recorded music.
Anyway, both

First, the music sounds different. For example, there is no rhythm section in *Kulture Jazz*and*Ten Freedom Summers*are very different from other jazz pieces devoted to the civil rights movements that I know (such as Max Roach's*Freedom Now. We Insist!*whose “Triptych: Prayer/Protest/Peace” is one of the rare jazz pieces that made me cry, or from Charles Mingus's “Fables of Faubus”).*Kulture Jazz*, and almost nothing as such in*Ten Freedom Summers.*And the pieces are definitely not built on the classical form (rhythmic/harmonic) we're now used to, either from listening to classical music, or from blues, or from the modal pieces played by Miles Davis, John Coltrane and others in the 50s-60s. Maybe not unlike latter pieces by Coltrane (Love Supreme, or Interstellar Space), Wadada Leo Smith's music is an abstract meditation about the place of an African-american musician in History.Then, although some parts of the concert seemed to be improvised, it all looked as if they played the music as it is written on a score. This was the more surprising for the drummer who, most always in jazz music, is left to imagining by himself how he should bring his playing to the music being created. (When drummers have scores, that's rarely drum scores, but more often that of the bass player, or simply the main theme with the chords changes.)

Even Pheeroan akLaff was obviously playing the drums as written on the score, but the compositions gave him a quite interesting role in the development of the music. Wadada Leo Smith had written long solos for the drums which began or ended the pieces. In fact, since the group that night had no bass player, but a cellist who played with the bow — anyway, Lindberg mostly plays with the bow on the CD too — the other musicians are not given the explicit harmonic/rhythmic pattern that a “walking bass” can impose on the music, so there's probably no point for the drummer to play a definite swing rhythm, which akLaff did not do.

And within Wadada Leo Smith's mostly meditative music, that was akLaff's playing — sometimes forceful, or with traces of military marches — that reminded us that Freedom is a fight.

An everyday-fight.

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