  We prove that every mapping torus of any free group endomorphism is
residually finite. We show how to use a not yet published result of E.
Hrushovski to extend our result to arbitrary linear groups. The proof uses
algebraic self-maps of affine spaces over finite fields. In particular, we
prove that when such a map is dominant, the set of its fixed closed scheme
points is Zariski dense in the affine space.
