Real Algebraic and Analytic Geometry |

Support functions, projections and Minkowski addition of Legendrian cycles.

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Submission: 2004, August 11.

*Abstract:
The structure of the space $\mathcal{LC}(\R^n \times S^{n-1})$ of
compactly supported integral Legendrian cycles
on $\R^n \times S^{n-1}$ is studied using Geometric Measure Theory. To
each such cycle $T$, a support function $h_T \in
L^1(S^{n-1},\mathbb{Z}[\R])$ is constructed. For almost all
$k$-dimensional linear subspaces $L$, a Legendrian cycle $\pi_L(T)$, whose
support function is the restriction of the support function of $T$ to
$L \cap S^{n-1}$, is
constructed. It is shown that there is a partial ring structure on
$\mathcal{LC}(\R^n \times S^{n-1})$, the multiplication being a
generalized Minkowski addition. An example of non-existence of the
Minkowski sum is given, but it is shown that the Minkowski sum does
exist after changing one of the summands by an arbitrarily small
linear map. Finally, mean projection formulas are formulated and
proved in the context of Legendrian cycles.*

Mathematics Subject Classification (2000): 49Q15, 53C65, 14P10.

Keywords and Phrases: Legendrian currents, subanalytic sets, support function, Minkowski addition, Lipschitz-Killing invariants.

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