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26. CJM 1999 (vol 51 pp. 49)

Ndombol, Bitjong; El haouari, M.
Algèbres quasi-commutatives et carrés de Steenrod
Soit $k$ un corps de caract\'eristique $p$ quelconque. Nous d\'efinissons la cat\'egorie des $k$-alg\`ebres de cocha\^{\i}nes fortement quasi-commutatives et nous donnons une condition n\'ecessaire et suffisante pour que l'alg\`ebre de cohomologie \`a coefficients dans $\mathbb{Z}_2$ d'un objet de cette cat\'egorie soit un module instable sur l'alg\`ebre de Steenrod \`a coefficients dans $\mathbb{Z}_2$. A tout c.w.\ complexe simplement connexe de type fini $X$ on associe une $k$-alg\`ebre de cocha\^{\i}nes fortement quasi-commutative; la structure de module sur l'alg\`ebre de Steenrod d\'efinie sur l'alg\`ebre de cohomologie de celle-ci co\"\i ncide avec celle de $H^*(X; \mathbb{Z}_2)$. We define the category of strongly quasi-commutative cochain $k$-algebras, where $k$ is a field of any characteristic $p$. We give a necessary and sufficient condition which enables the cohomology algebra with $\mathbb{Z}_2$-coefficients of an object in this category to be an unstable module on the $\mathbb{Z}_2$-Steenrod algebra. To each simply connected c.w.\ complex of finite type $X$ is associated a strongly quasi-commutative model and the module structure over the $\mathbb{Z}_2$-Steenrod algebra defined on the cohomology of this model is the usual structure on $H^*(X; \mathbb{Z}_2)$.

Keywords:algèbres de cocha\^{\i}nes (fortement) quasi-commutatives, $T (V)$-modèle, carrés de Steenrod, quasi-isomorphisme
Categories:55P62, 55S05

27. CJM 1998 (vol 50 pp. 1048)

Goerss, P. G.; Jardine, J. F.
Localization theories for simplicial presheaves
Most extant localization theories for spaces, spectra and diagrams of such can be derived from a simple list of axioms which are verified in broad generality. Several new theories are introduced, including localizations for simplicial presheaves and presheaves of spectra at homology theories represented by presheaves of spectra, and a theory of localization along a geometric topos morphism. The $f$-localization concept has an analog for simplicial presheaves, and specializes to the $\hbox{\Bbbvii A}^1$-local theory of Morel-Voevodsky. This theory answers a question of Soul\'e concerning integral homology localizations for diagrams of spaces.

Categories:55P60, 19E08, 18F20

28. CJM 1998 (vol 50 pp. 845)

Scheerer, H.; Tanré, D.
Lusternik-Schnirelmann category and algebraic $R$-local homotopy theory
In this paper, we define the notion of $R_{\ast}$-$\LS$ category associated to an increasing system of subrings of $\Q$ and we relate it to the usual $\LS$-category. We also relate it to the invariant introduced by F\'elix and Lemaire in tame homotopy theory, in which case we give a description in terms of Lie algebras and of cocommutative coalgebras, extending results of Lemaire-Sigrist and F\'elix-Halperin.

Categories:55P50, 55P62

29. CJM 1998 (vol 50 pp. 342)

Giraldo, Antonio
Shape fibrations, multivalued maps and shape groups
The notion of shape fibration with the near lifting of near multivalued paths property is studied. The relation of these maps---which agree with shape fibrations having totally disconnected fibers---with Hurewicz fibrations with the unique path lifting property is completely settled. Some results concerning homotopy and shape groups are presented for shape fibrations with the near lifting of near multivalued paths property. It is shown that for this class of shape fibrations the existence of liftings of a fine multivalued map, is equivalent to an algebraic problem relative to the homotopy, shape or strong shape groups associated.

Keywords:Shape fibration, multivalued map, homotopy groups, shape, groups, strong shape groups
Categories:54C56, 55P55, 55Q05, 55Q07, 55R05

30. CJM 1997 (vol 49 pp. 1323)

Sankaran, Parameswaran; Zvengrowski, Peter
Stable parallelizability of partially oriented flag manifolds II
In the first paper with the same title the authors were able to determine all partially oriented flag manifolds that are stably parallelizable or parallelizable, apart from four infinite families that were undecided. Here, using more delicate techniques (mainly K-theory), we settle these previously undecided families and show that none of the manifolds in them is stably parallelizable, apart from one 30-dimensional manifold which still remains undecided.

Categories:57R25, 55N15, 53C30

31. CJM 1997 (vol 49 pp. 855)

Smith, Samuel Bruce
Rational Classification of simple function space components for flag manifolds.
Let $M(X,Y)$ denote the space of all continous functions between $X$ and $Y$ and $M_f(X,Y)$ the path component corresponding to a given map $f: X\rightarrow Y.$ When $X$ and $Y$ are classical flag manifolds, we prove the components of $M(X,Y)$ corresponding to ``simple'' maps $f$ are classified up to rational homotopy type by the dimension of the kernel of $f$ in degree two cohomology. In fact, these components are themselves all products of flag manifolds and odd spheres.

Keywords:Rational homotopy theory, Sullivan-Haefliger model.
Categories:55P62, 55P15, 58D99.
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