无法删除附加到事件上的匿名代理

//IT WON'T WORK!

var changed = false;
a.PropertyChanged += (sender, e) => changed = true;
....
a.PropertyChanged -= (sender, e) => changed = true;
if(changed)
  ....

---

//This one works:

var changed = false;

PropertyChangedEventHandler onchange = delegate { changed = true; };

a.PropertyChanged += onchange;

...

a.PropertyChanged -= onchange;

if(changed)

 ...