Promela Reference -- np_(5)

### `Promela` | ### `Predefined` | ### `np_(5)`

`NAME`
`np_` - a predefined read-only boolean variable.

`SYNTAX`
`np_`

`DESCRIPTION`
This variable is set to `true` by the system in all global system states that are not marked as progress states, and to `false` in all other states. The system is in a progress state if at least one active process is at a local control state that was marked with a `progress` label, or if a `trace` declaration marks the global state as a a `progress` state.

This predefined variable is meant to be used inside `never` claims only.

`EXAMPLES`
Catch non-progress cycles with an explicit `never` claim:

    never {	/* <>[] np_ */
    	do
    	:: skip
    	:: np_ -> break
    	od;
    accept:	do
    	:: np_
    	od
    }

`SEE ALSO`
`ltl(1)`, `progress(2)`, `never(2)`.

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