In this introductory textbook, a revised and extended version of
well-known lectures by L. Hörmander from 1986, four chapters are devoted
to weak solutions of systems of conservation laws. Apart from that the
book only studies classical solutions. Two chapters concern the
existence of global solutions or estimates of the lifespan for solutions
of nonlinear perturbations of the wave or Klein-Gordon equation with
small initial data. Four chapters are devoted to microanalysis of the
singularities of the solutions. This part assumes some familiarity with
pseudodifferential operators which are standard in the theory of linear
differential operators, but the extension to the more exotic classes of
opertors needed in the nonlinear theory is presented in complete detail.