[ServiceContract(Namespace = "http://Microsoft.WorkflowServices.Samples")]
public interface ICalculator
{
    [OperationContract()]
    int PowerOn();
    [OperationContract()]
    int Add(int value);
    [OperationContract()]
    int Subtract(int value);
    [OperationContract()]
    int Multiply(int value);
    [OperationContract()]
    int Divide(int value);
    [OperationContract()]
    void PowerOff();
}
