Nonembedding and nonextension results in special holonomy
  Constructions of metrics with special holonomy by methods of exterior differential systems are reviewed and the interpretations of these construction as `flows' on hypersurface geometries are considered.   It is shown that these hypersurface 'flows' are not generally well-posed for smooth initial data and counterexamples to existence are constructed. 
Robert L. Bryant
math.DG