A new mixed formulation recently proposed for linear problems is extended to quasilinear second-order elliptic problems. This new formulation expands the standards mixed formulation in the sense that three variables are explicitly treated; i.e., the scalar unknown, its gradient, and its flux(the coefficient times the gradient). Based on this formulation, mixed finite element approximations of the quasilinear problems are established. Existence and uniqueness of the solution of the mixed formulation and its discretization are demonstrated. Optimal order error estimates in L~p and H~-s are obtained for the mixed approximations.
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