VarMapFixpoint.bpl(13,5): Error BP5005: This loop invariant might not be maintained by the loop.
Execution trace:
    VarMapFixpoint.bpl(7,3): start
    VarMapFixpoint.bpl(12,3): LoopHead
    VarMapFixpoint.bpl(16,3): LoopBody

Boogie program verifier finished with 1 verified, 1 error