On the blowup and lifespan of smooth solutions to a class of 2-D nonlinear wave equations with small initial data

Jun Li, Ingo Witt, Huicheng Yin

We are concerned with a class of two-dimensional nonlinear wave equations $\p_t^2u-÷(c^2(u)\na u)=0$ or $\p_t^2u-c(u)÷(c(u)\na u)=0$ with small initial data $(u(0,x),\p_tu(0,x))=(\…