git-issue-1957.dfy(4,23): Info: autocontracts:
   ghost var Repr: set<object?>
git-issue-1957.dfy(5,20): Info: autocontracts:
   reads this, Repr
   ensures Valid() ==> this in Repr
git-issue-1957.dfy(5,20): Info: autocontracts:
   this in Repr && null !in Repr

Dafny program verifier finished with 1 verified, 0 errors
