public override bool Merge(ModelCommand other)
 {
     return false;
 }
 public override bool Merge(ModelCommand other)
 {
     var s = other as NodeValueCommmand;
     if (s != null
         && s != this
         && s.Change.Node == Change.Node)
     {
         ((NodeValueChange)Change).OldValue = ((NodeValueChange)s.Change).OldValue;
         return true;
     }
     return false;
 }
 public abstract bool Merge(ModelCommand other);