NatTypes.dfy(35,12): Error: value assigned to a nat must be non-negative
Execution trace:
    (0,0): anon0
    NatTypes.dfy(23,5): anon10_LoopHead
    (0,0): anon10_LoopBody
    NatTypes.dfy(23,5): anon11_Else
    (0,0): anon12_Then
NatTypes.dfy(10,5): Error: value assigned to a nat must be non-negative
Execution trace:
    (0,0): anon0
NatTypes.dfy(43,14): Error: assertion violation
Execution trace:
    (0,0): anon0
    (0,0): anon4_Then
NatTypes.dfy(45,14): Error: assertion violation
Execution trace:
    (0,0): anon0
    (0,0): anon4_Then
NatTypes.dfy(62,16): Error: assertion violation
Execution trace:
    (0,0): anon0
    (0,0): anon3_Then
NatTypes.dfy(76,16): Error: assertion violation
Execution trace:
    (0,0): anon0
    (0,0): anon5_Else
    (0,0): anon6_Then
NatTypes.dfy(94,22): Error: value assigned to a nat must be non-negative
Execution trace:
    (0,0): anon0
    (0,0): anon3_Then
NatTypes.dfy(109,45): Error: value assigned to a nat must be non-negative
Execution trace:
    (0,0): anon0
    (0,0): anon6_Else
    (0,0): anon7_Else
    (0,0): anon8_Then
NatTypes.dfy(132,35): Error: value assigned to a nat must be non-negative
Execution trace:
    (0,0): anon0
    (0,0): anon3_Then

Dafny program verifier finished with 15 verified, 9 errors