Géométrie sous-riemannienne
The paper presents new quasicontinuous selection theorem for continuous multifunctions with closed values, being an arbitrary topological space. It is known that for with the Vietoris topology there is no continuous selection. The result presented here enables us to show that there exists a quasicontinuous and upperlower-semicontinuous selection for this space. Moreover, one can construct a selection whose set of points of discontinuity is nowhere dense.
In the present paper, we consider the class of control systems which are induced by the action of a semi-simple Lie group on a manifold, and we give a sufficient condition which insures that such a system can be steered from any initial state to any final state by an admissible control. The class of systems considered contains, in particular, essentially all the bilinear systems. Our condition is semi-algebraic but unlike the celebrated Kalman criterion for linear systems, it is not necessary. In...
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