(** ** Proofs of internal step safety and simulation*)

Lemma cmachine_step_invariant:
forall tpc mc trc tpc' mc' trc' tpc'' trc'' mc'' U U' U'' n
(HstepN: corestepN n
(U, trc, tpc) mc (U', trc',tpc') mc')
(Hstep: cmachine_step (U', trc', tpc') mc' (U'',trc'', tpc'') mc''),
invariant tpc.