PolyList.bpl(48,3): Error BP5001: This assertion might not hold.
Execution trace:
    PolyList.bpl(33,7): anon0
PolyList.bpl(66,3): Error BP5001: This assertion might not hold.
Execution trace:
    PolyList.bpl(55,7): anon0

Boogie program verifier finished with 0 verified, 2 errors