Iterators.dfy(40,21): Error: a precondition for this call could not be proved
Iterators.dfy(4,9): Related location: this is the precondition that could not be proved
Iterators.dfy(89,13): Error: assertion might not hold
Iterators.dfy(103,21): Error: assertion might not hold
Iterators.dfy(106,13): Error: assertion might not hold
Iterators.dfy(119,15): Error: assertion might not hold
Iterators.dfy(150,15): Error: assertion might not hold
Iterators.dfy(155,23): Error: a precondition for this call could not be proved
Iterators.dfy(125,9): Related location: this is the precondition that could not be proved
Iterators.dfy(177,27): Error: assertion might not hold
Iterators.dfy(208,6): Error: an assignment to _new is only allowed to shrink the set
Iterators.dfy(212,20): Error: assertion might not hold
Iterators.dfy(234,20): Error: assertion might not hold
Iterators.dfy(413,16): Error: this invariant could not be proved to be maintained by the loop
 Related message: loop invariant violation
Iterators.dfy(414,21): Error: this invariant could not be proved to be maintained by the loop
 Related message: loop invariant violation
Iterators.dfy(415,21): Error: this invariant could not be proved to be maintained by the loop
 Related message: loop invariant violation
Iterators.dfy(436,18): Error: this invariant could not be proved to be maintained by the loop
 Related message: loop invariant violation
Iterators.dfy(437,23): Error: this invariant could not be proved to be maintained by the loop
 Related message: loop invariant violation
Iterators.dfy(438,23): Error: this invariant could not be proved to be maintained by the loop
 Related message: loop invariant violation
Iterators.dfy(459,16): Error: this invariant could not be proved to be maintained by the loop
 Related message: loop invariant violation
Iterators.dfy(460,21): Error: this invariant could not be proved to be maintained by the loop
 Related message: loop invariant violation
Iterators.dfy(461,21): Error: this invariant could not be proved to be maintained by the loop
 Related message: loop invariant violation
Iterators.dfy(470,4): Error: possible violation of yield-ensures condition
Iterators.dfy(451,21): Related location: this proposition could not be proved
Iterators.dfy(251,9): Error: decreases clause might not decrease
Iterators.dfy(274,9): Error: decreases clause might not decrease
Iterators.dfy(284,31): Error: decreases clause might not decrease
Iterators.dfy(296,9): Error: cannot prove termination; try supplying a decreases clause
Iterators.dfy(317,9): Error: cannot prove termination; try supplying a decreases clause
Iterators.dfy(326,31): Error: cannot prove termination; try supplying a decreases clause
Iterators.dfy(343,9): Error: decreases clause might not decrease
Iterators.dfy(353,31): Error: cannot prove termination; try supplying a decreases clause
Iterators.dfy(370,9): Error: decreases clause might not decrease

Dafny program verifier finished with 35 verified, 30 errors
