PredExpr.dfy(7,11): Error: assertion violation
Execution trace:
    (0,0): anon0
    (0,0): anon4_Else
PredExpr.dfy(39,14): Error: value assigned to a nat must be non-negative
Execution trace:
    (0,0): anon0
    (0,0): anon7_Else
    (0,0): anon8_Else
PredExpr.dfy(52,16): Error: assertion violation
Execution trace:
    (0,0): anon0
PredExpr.dfy(77,13): 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