Matter Collineations of Plane Symmetric Spacetimes
  This paper is devoted to the study of matter collineations of plane symmetric spacetimes (for a particular class of spacetimes) when the energy-momentum tensor is non-degenerate. There exists many interesting cases where we obtain proper matter collineations. The matter collineations in these cases are {\it four}, \emph{five}, {\it six}, \emph{seven} and {\it ten} with some constraints on the energy-momentum tensor. We have solved some of these constraints to obtain solutions of the Einstein field equations. 
M. Sharif and Nousheen Ilyas