Abstract
In this paper I will give a survey on a priori estimates such as the Gårding, Sharp-Gårding, Melin, Hörmander and the Fefferman–Phong inequalities for pseudodifferential operators, discuss some generalizations and open problems in some directions. Finally, I will describe what is known at present in the case of systems of pseudodifferential operators, the latter being a still largely open and unexplored area.
I wish to thank the organizers of the ISAAC conference 2017 held in Växjö (Sweden), and in particular Luigi Rodino and Joachim Toft
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Parmeggiani, A. (2018). Almost-Positivity Estimates of Pseudodifferential Operators. In: Rodino, L., Toft, J. (eds) Mathematical Analysis and Applications—Plenary Lectures. ISAAC 2017. Springer Proceedings in Mathematics & Statistics, vol 262. Springer, Cham. https://doi.org/10.1007/978-3-030-00874-1_4
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