Propagation of singularities along a characteristic boundary for a model problem of shell theory and relation with the boundary layer

We consider the propagation of singularities for a differential system which constitutes a simplified model of thin shells with developable middle surface (parabolic case). Extensions of the solutions out of the domain allow us to consider either boundary or internal singularities. The properties of propagation of singularities and their relation with the structure of the boundary layers are given. We remove a mistake in [2], Section 6.1, concerning the analyticity of solutions (in fact they are in the Gevrey class of order 3).