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# Homology, Homotopy and Applications

## Volume 4 (2002)

### Number 2

### The Roos Festschrift volume

### The Riemann tensor for nonholonomic manifolds

Pages: 397 – 407

DOI: http://dx.doi.org/10.4310/HHA.2002.v4.n2.a18

#### Author

#### Abstract

For every *nonholonomic* manifold, i.e., manifold with non-integrable distribution the analog of the Riemann tensor is introduced. It is calculated here for the contact and Engel structures: for the contact structure it vanishes (another proof of Darboux’s canonical form); for the Engel distribution the target space of the tensor is of dimension 2. In particular, the Lie algebra preserving the Engel distribution is described.

The tensors introduced are interpreted as modifications of the Spencer cohomology and, as such, provide with a new way to solve partial differential equations. Goldschmidt’s criteria for formal integrability (vanishing of certain Spencer cohomology) are only applicable to “one half” of all differential equations, the ones whose symmetries are induced by point transformations. Lie’s theorem says that the “other half” consists of differential equations whose symmetries are induced by contact transformations. Therefore, we can now extend Goldschmidt’s criteria for formal integrability to all differential equations.

#### Keywords

Engel distribution, Lie algebra cohomology, Cartan prolongation, Riemann tensor, nonholonomic manifold

#### 2010 Mathematics Subject Classification

17A70, 17B35