  We introduce a spacetime discretization of the Dirac equation that has the
form of a quantum automaton and that is invariant upon changing the
representation of the Clifford algebra, as the Dirac equation itself. Our
derivation follows Dirac's original one: We required that the square of the
discrete Dirac scheme be what we define as an acceptable discretization of the
Klein-Gordon equation. Contrary to standard lattice gauge theory in discrete
time, in which unitarity needs to be proven, we show that the quantum automaton
delivers naturally unitary Wilson fermions for any choice of Wilson's
parameter.
