PredExpr.dfy(7,12): Error: assertion violation
Execution trace:
    (0,0): anon0
    (0,0): anon3_Else
PredExpr.dfy(39,15): Error: value assigned to a nat must be non-negative
Execution trace:
    (0,0): anon0
    (0,0): anon5_Else
    (0,0): anon6_Else
PredExpr.dfy(52,17): Error: assertion violation
Execution trace:
    (0,0): anon0
PredExpr.dfy(77,14): Error: assertion violation
Execution trace:
    (0,0): anon0
    (0,0): anon8_Else
    (0,0): anon3
    PredExpr.dfy(76,20): anon10_Else
    (0,0): anon6

Dafny program verifier finished with 11 verified, 4 errors