R. Freund, Y. Rogozhin, S. Verlan:
"P Systems with Minimal Left and Right Insertion and Deletion";
in: "11th Int. Conference on Unconventional Computation and Natural Computation", J. Durand-Lose et al. (ed.); Springer LNCS, Heidelberg, 2012, ISBN: 978-3-642-32893-0, 82 - 93.