We introduce the notion of a ghost characteristic for nonlocal differential equations. Ghosts are essential for maintaining the validity of the Jacobi identity for the characteristics of nonlocal vector fields.
Bibliographical noteFunding Information:
Acknowledgments: The research of P.J. Olver was supported in part by NSF Grant DMS 98–03154. J.P. Wang gratefully acknowledges the support from Netherlands Organization for Scientific Research (NWO) for this research.
Copyright © 2002 by P J Olver, J A Sanders and J P Wang.