Life-span of classical solutions to two dimensional fully nonlinear wave equations

In two-space-dimensional case, we get the lower bound of the life-span of classical solutions to the Cauchy problem with small initial data for fully nonlinear wave equations of the form □u=F(u,Du,DxDu)□u=F(u,Du,DxDu) in which F(λˆ)=O(|λˆ|3) in a neighbourhood of λˆ=0, and ∂u3F(0,0,0)=0. For the purpose, some refined estimates including Strichartz estimates are needed in the paper.