gistfile1.cs

public abstract class ObservableBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void RaisePropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    protected Formula<T> Formula<T>(Func<T> formula, params string[] dependencyProperties)
    {
        return new Formula<T>(this, formula, dependencyProperties);
    }
}