```clafer
TrafficLight
    red : Lamp
    yellow : Lamp 
    green : Lamp
    leftGreenArrow : Lamp ?
        [ LeftGreenArrow ]
        [ leftArrow ]        
    rightGreenArrow : Lamp ?
        [ RightGreenArrow ]
    arrowsOff ?
    [ arrowsOff <=> (no leftGreenArrow.on) && (no leftGreenArrow.flashing) ]
    [ arrowsOff <=> (no rightGreenArrow.on) && (no rightGreenArrow.flashing) ]
    emergencyVehicle ?
```

```clafer
xor TrafficSignals
    [ emergencyVehicle && allWayYellow => allYellow ]
    [ emergencyVehicle && no allWayYellow => warning ]
    proceed
        [ no emergencyVehicle ]
        [ red.off ]
        [ yellow.off ]
        [ green.on ]
        [ leftGreenArrow => leftGreenArrow.on ]
        [ rightGreenArrow => rightGreenArrow.on ]
    prepareToStop
        [ no emergencyVehicle ]
        [ red.off ]
        [ yellow.on ]
        [ green.off ]
        [ arrowsOff ]
    stop
        [ no emergencyVehicle ]
        [ red.on ]
        [ yellow.off ]
        [ green.off ]
        [ arrowsOff ]
    warning
        [ red.off ]
        [ yellow.flashing ]
        [ green.off ]
        [ arrowsOff ]
    prepareToGo
        [ no emergencyVehicle ]
        [ redAndYellowToGreen ]
        [ red.on ]
        [ yellow.on ]
        [ green.off ]
        [ arrowsOff ]
    allStop
        [ no emergencyVehicle ]
        [ allWayFlashingRedAsStop  ]
        [ red.flashing ]
        [ yellow.off ]
        [ green.off ]
        [ arrowsOff ]
    allYellow
        [ allWayYellow  ]
        [ red.off ]
        [ yellow.flashing ]
        [ green.off ]
        [ arrowsOff ]
    advancedLeft
        [ no emergencyVehicle ]
        [ advancedOrExtendedLeft  ]
        [ red.on ]
        [ yellow.off ]
        [ greenFlashing => green.flashing ]
        [ leftArrow => leftGreenArrow.flashing && green.off ]
    extendedLeft
        [ no emergencyVehicle ]
        [ advancedOrExtendedLeft  ]
        [ red.on ]
        [ yellow.off ]
        [ greenFlashing => green.flashing ]
        [ leftArrow => leftGreenArrow.flashing && green.off ]
```

```clafer
abstract xor Lamp
    on
    off
    flashing
```

```clafer
TrafficLightSystem
    Lamps
        LeftGreenArrow ?
        RightGreenArrow ?
    redAndYellowToGreen ?
    allWayFlashingRedAsStop ?
    allWayYellow ?
    xor advancedOrExtendedLeft ?
        greenFlashing
        leftArrow
```

Let's try it out.
Again, assert certain signals and see what are the states of the lamps. 
E.g., when you turn all features off and assume the presence or absence of an emergencyVehicle:

```clafer
[ no LeftGreenArrow ]
[ no RightGreenArrow ]
[ no redAndYellowToGreen ]
[ no allWayFlashingRedAsStop ]
[ no allWayYellow ]
[ no advancedOrExtendedLeft ]

[ emergencyVehicle ]
```

<table>
<tr>
<td>

```{.clafer .config}
```

</td>
<td>

```{.clafer .ide}
```

</td>
</tr>
</table>

```{.clafer .stats}
```

```{.clafer .links}
```

> Back to [linking signals and lamps](linking signals and lamps#conclusion-of-part-ii).