  We present a formulation of quantum circuits where the focus is set on
whether a given circuit (made of unitary operators and projective measurements
with definite outcomes) does reflect an actually realizable physical
experiment. In order to do this, we introduce verifications statements which
are purely epistemic assertions indicating whether a outcome is possible at
some point and develop our formalism which, in the end, consists in a set of
logical rules about verification statements. Finally, we argue that our
formalism provides a Lorentz-invariant realistic formulation of quantum
circuits and illustrate this by considering a circuit corresponding to Hardy's
paradox and showing how our formalism prevents making contradictory assertions
regarding our knowledge about the circuit.
