public TraceDisposer(TraceOperator <T> parent, IDisposable inner, int id)
 {
     _parent = parent;
     _inner  = inner;
     _id     = id;
 }
 public TraceObserver(TraceOperator <T> parent, IObserver <T> inner, int id)
 {
     _parent = parent;
     _inner  = inner;
     _id     = id;
 }