\item \lect
Given a 2-bit bitvector $x$, we want to check whether it is possible that $x + 1 < x - 1$.

The following python script returns \texttt{sat}. Explain the error in the script and expand it such that it correctly prints \texttt{unsat}.

  \vskip7em
  \begin{pythonSourceCode}

      from z3 import *

      solver = Solver()

      bvX  = BitVec("bvX", 2)

      solver.add(bvX + 1 < bvX - 1)

      solver.add(BVAddNoOverflow(bvX, 1, True))
      solver.add(BVSubNoUnderflow(bvX, 1, True))

      result = solver.check()
      print(result)
      if result == sat:
          print(solver.model())

  \end{pythonSourceCode}
