Abstract
The aim of this article is to provide a new approach for the classical Feerman-Phong inequality and some other related inequalities concerning pseudo- dierential operators. The idea is to conjugate these estimates with respect to the FBI transform and obtain equivalent formulations which require only a few deriva- tives of the symbol. Modulo some integration by parts, these are reduced to certain decomposition results for C1,1, respectively C3,1 functions. As a byproduct of this method we get to extend the inequalities to (possibly sharp) classes of symbols with limited smoothness.

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