Wave Maps and Ill-posedness of their Cauchy Problem -- On the Global Behavior of Classical Solutions to Coupled Systems of Semilinear Wave Equations -- Decay and Global Existence for Nonlinear Wave Equations with Localized Dissipations in General Exterior Domains -- Global Existence in the Cauchy Problem for Nonlinear Wave Equations with Variable Speed of Propagation -- On the Nonlinear Cauchy …