Approximation for Frobenius algebraic equations in Witt vectors

We prove an approximation property for solutions to difference equations in excellent discrete valuation rings satisfying an appropriate Hensel's lemma, analog to a theorem of Greenberg [M. Greenberg, Rational points in henselian discrete valuation rings, Publ. Math. Inst. Hautes Études Sci. 31 (1966) 59–64]. In the case of Witt vectors we obtain a Nullstellensatz for Frobenius algebraic equations.