Switch Item ON when Temperature <=0°

I need a rule that turns VirtualItemFrost On when Temperature is <=0 and turn OFF when over 0.
Can anybody help me?
Temperature comes from Yahoo Weather Binding, Wetterinformation_Temperatur

rule "Temperature"
when
    Item Wetterinformation_Temperatur changed
then
    if(Wetterinformation_Temperatur.state <= 0) {
      if (VirtualItemFrost.state != OFF) VirtualItemFrost.sendCommand(OFF)
    } else {
      if (VirtualItemFrost.state != ON) VirtualItemFrost.sendCommand(ON)
    }
end

Thanks for help, i try it.