The object of this paper is
to develop a regularity theory for equations of mean curvature type in two
independent variables. An equation of mean curvature type in two independent
variables is defined to be an equation of the form
on a domain Ω ⊂ R2, where the functions aij, b satisfy special structural conditions.
Namely, we require that (i) (1 + |Du|2)−1∕2b(x,u,Du) is bounded by a fixed constant
(independent of u), and (ii) the quadratic form ∑
i,j=12aij(x,u,Du)ξiξj is bounded
from above and below in terms of the quadratic form ∑
i,j=12gij(Du)ξiξj, where
gij(Du) = δij −DiuDju∕(1 + |Du|2), i,j = 1,2, are the coefficients of the minimal
surface equation.
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