COAREA FORMULA FOR FUNCTIONS ON TWO-STEP CARNOT GROUPSWITH SUB-LORENTZIAN STRUCTURE
We consider C1-functions defined on two-step Carnot groups with sub-Lorentzian structure defined by one horizontal direction with negative square of length along it, and prove the non-holonomic coarea formula. Result on correctness of problem statement, that is, the level sets should be space-like, is of independent interest.