<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Iakovos Androulidakis</style></author><author><style face="normal" font="default" size="100%">Omar Mohsen</style></author><author><style face="normal" font="default" size="100%">Robert Yuncken</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">A pseudodifferential calculus for maximally hypoelliptic operators and the Helffer-Nourigat conjecture</style></title></titles><dates><year><style  face="normal" font="default" size="100%">Submitted</style></year></dates><urls><web-urls><url><style face="normal" font="default" size="100%">https://arxiv.org/abs/2201.12060</style></url></web-urls></urls><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;span&gt;Given a filtration of the module of vector fields on a smooth manifold, we define a pseudodifferential calculus where the order of a vector field is given by the filtration. We show that pseudodifferential operators have a well-defined principal symbol for a subset of the unitary representations of the osculating groups. We prove a Rockland-type theorem, showing that the invertibility of the principal symbol is equivalent to maximal hypoellipticity. This answers affirmatively a conjecture due to Helffer and Nourrigat.&lt;/span&gt;</style></abstract></record></records></xml>