  Cook's theorem is commonly expressed such as any polynomial time-verifiable
problem can be reduced to the SAT problem. The proof of Cook's theorem consists
in constructing a propositional formula A(w) to simulate a computation of TM,
and such A(w) is claimed to be CNF to represent a polynomial time-verifiable
problem w. In this paper, we investigate A(w) through a very simple example and
show that, A(w) has just an appearance of CNF, but not a true logical form.
This case study suggests that there exists the begging the question in Cook's
theorem.
