A Blowup Solution of Multispeed Klein-Gordon System in Space Dimension Two with Small Initial Data

We find an example to illustrate that the first nondegeneracy condition of (1.2) is actually needed in proving the global exsitence of 2D multispeed Klein-Gordon system with small initial data (See [3]). We construct a collection of special Klein-Gordon dispersive relations and by iterating the corresponding profiles we can find a blowup in finite time.