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Given a compact manifold , an integer and an exponent , we prove that the class of smooth maps on the cube with values into is dense with respect to the strong topology in the Sobolev space when the homotopy group of order is trivial. We also prove density of maps that are smooth except for a set of dimension , without any restriction on the homotopy group of .
J. Keesling has shown that for connected spaces the natural inclusion of in its Stone-Čech compactification is a shape equivalence if and only if is pseudocompact. This paper establishes the analogous result for strong shape. Moreover, pseudocompact spaces are characterized as spaces which admit compact resolutions, which improves a result of I. Lončar.
Let K be a CW-complex of dimension 3 such that H³(K;ℤ) = 0, and M a closed manifold of dimension 3 with a base point a ∈ M. We study the problem of existence of a map f: K → M which is strongly surjective, i.e. such that MR[f,a] ≠ 0. In particular if M = S¹ × S² we show that there is no f: K → S¹ × S² which is strongly surjective. On the other hand, for M the non-orientable S¹-bundle over S² there exists a complex K and f: K → M such that MR[f,a] ≠ 0.
Let K be a CW-complex of dimension 3 such that H 3(K;ℤ) = 0 and
the orbit space of the 3-sphere
with respect to the action of the quaternion group Q 8 determined by the inclusion Q 8 ⊆
. Given a point a ∈
, we show that there is no map f:K →
which is strongly surjective, i.e., such that MR[f,a]=min(g −1(a))|g ∈ [f] ≠ 0.
Given a model 2-complex K P of a group presentation P, we associate to it an integer matrix ΔP and we prove that a cellular map f: K P → S 2 is root free (is not strongly surjective) if and only if the diophantine linear system ΔP Y =
(f) has an integer solution, here
(f)is the so-called vector-degree of f
On construit et classifie à conjugaison équivariante près toutes les formes de contact invariantes sur un fibré principal en cercles ( compact). Si , les formes obtenues induisent sur des formes de contact dans chaque classe d’homotopie de 1-formes sans zéros : on en déduit que admet une infinité de structures de contact non isomorphes.
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