New Post: "reads" and "termination" errors

Hi,

I have some "reads" and "termination" errors for the following code (http://rise4fun.com/Dafny/zHqA):

class Tree{ 
    var left : Tree;
    var right : Tree;
    var val : int;

    ghost var repr: set <object>;

  function Valid(): bool
    reads this, repr;
  {
    this in repr &&
    ((left == null && right == null) ||
    (((left != null) ==> (left.repr < repr && this !in left.repr && left.Valid())) &&
    ((right != null) ==> (right.repr < repr && this !in right.repr && right.Valid()))
    ))
  }
}

i.e. on line

    (((left != null) ==> (left.repr < repr && this !in left.repr && left.Valid())) &&

and

    ((right != null) ==> (right.repr < repr && this !in right.repr && right.Valid()))

However, if I add "left in repr" and "right in repr", these errors go away. These two are, in my mind, logically redundant, as "left in repr" can be inferred by "left.repr < repr" and "left in left.repr".

What did I miss here ?

Thanks in advance.

best,
Yuhui