A possible generalization of plane fronted waves with parallel rays
(gpp-wave) fall into a more general class of metrics admitting parallel null
1-planes. For gpp-wave metric, the zero-curvature condition is given, the
Killing-Yano tensors of order two and three are found and the corresponding
Killing tensors are constructed. Henceforth, the compatibility between
geometric duality and non-generic symmetries is presented.Comment: 11 pages, LaTeX, to be published in Il Nuovo Cimento
