Existing Proof Methods Simulation in CompCert [Leroy et al. J Source state (S, (S,Σ) (S,∑") observable event(e.g. I/O) Target state (T,o) T",′Existing Proof Methods: Simulation in CompCert (T, ) (S, ) (S’ , ’) (T’, ’) * (S’’, ’’) (T’’, ’’) e e * … …    [Leroy et al.] Source state Target state observable event (e.g. I/O)