public void Erase()
 {
     if (LastContent.IsErasable)
     {
         LastContent = new PaperContent(string.Empty, true);
     }
 }
 public void Write(string content, IWritingUtensil utensil)
 {
     if (LastContent.Text != string.Empty)
     {
         PaperContent.Add(LastContent);
     }
     LastContent = new PaperContent(content, (utensil is IErasable));
 }
 public Paper()
 {
     PaperContent = new List <PaperContent>();
     LastContent  = new PaperContent(string.Empty, true);
 }