Ultra-hyperbolic pde and F theory

[MathematicalPhysicist]

Is there a conncetion between Fritz john's ultra-hyperbolic pde, which is the equation:

$$u_{tt}+u_{\tau \tau} = u_{xx}+u_{yy}$$

I mean F theory has another dimension of time, and the above pde has also another time variable with regards to the simple wave pde.

Any literature on this?

Thanks.

 

[MathematicalPhysicist]

Btw, any introductory books in the net regarding F theory?, I don't mind 800-1000 pages books... :-D