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A remark on sums of squares of complex vector fields

Michael Christ
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Abstract

This note is a comment on a recent paper by J. J. Kohn. We give an example of a second order partial differential operator, expressed as a sum of squares of complex vector fields satisfying the bracket condition, that is not hypoelliptic.

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Michael Christ. 2005-03-23. A remark on sums of squares of complex vector fields. https://arxiv.org/abs/math/0503506

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