When a prologue wishes to start a continuation (check) it hands over to the guard the corresponding epilogue ob-ject to be executed (relay). The epilogue will be run (en-act) only when the sluice is free, meaning that the control-ling guard is locked. Initially the sluice is free, i.e. all guarded sections are inactive. The free-state of the sluice is canceled when a guarded section becomes active (enter),