Classes.dfy(64,11): Error: assertion violation
Execution trace:
    (0,0): anon0
Classes.dfy(40,5): Error: possible violation of function precondition
Execution trace:
    (0,0): anon0
    (0,0): anon7_Else
    (0,0): anon8_Else

Dafny program verifier finished with 8 verified, 2 errors