1. Applications of Lie Groups to Differential Equations;Olver,1986
2. Infinitesimal Group Transformation Methods for Differential Equations;Bluman,1989
3. On invariance properties of the wave equation;Bluman;J. Math. Phys.,1987
4. A Bäcklund Transformation Theory Generating Chains of Second-Order Linear PDE's and Related Solution Sequences;Bluman,1987
5. G. Bluman and G. Reid, Sequences of related linear PDES, J. Math. Anal. Appl., to appear.