CONSTANTS
  Files = {f1, f2}
  Contents = {c1, c2}
  MaxBackups = 3
  KeepCount = 2
  MaxSteps = 6
  Nil = Nil

INIT Init
NEXT Next

CHECK_DEADLOCK FALSE

INVARIANTS
  TypeOk
  BackupSnapshotsValid
  VerifyIntegrity
  RetentionInvariant
  HistoryConsistency
  BackupIdValid