Twice.dfy(26,21): Error: assertion violation
Execution trace:
    (0,0): anon0
    Twice.dfy(22,12): anon3_Else
Twice.dfy(34,31): Error: possible violation of function precondition
Execution trace:
    (0,0): anon0
    (0,0): anon10_Else
    (0,0): anon11_Then

Dafny program verifier finished with 2 verified, 2 errors
