I need to prove that if $SAT\notin Size(2^{n/100})$ then CorrectSATSolver$\in P$.

Where CorrectSATSolver $= \{C | C(\varphi) = 1 \iff \varphi$ is satisfiable$\}$. In other words, CorrectSATSolver problem is as follows: Given a circuit C, decide if the circuit C solves the SAT problem.

I don't understand how to use the assumption.

I have already proven in class thet CorrectSATSolver $\in coNP$, I'm not sure if it helps.

I would very appreciate any help. Thank yoy

  • $\begingroup$ What is the definition of $Size(f(n))$? $\endgroup$
    – plshelp
    Commented Apr 18, 2022 at 21:39
  • 1
    $\begingroup$ This is a nice puzzle. I suggest spending a few more hours on it. The solution is very short. $\endgroup$ Commented Apr 19, 2022 at 5:16
  • $\begingroup$ @plshelp Size(f(n)) is the set of decision problems that can be solved by f(n)-sized circuit families. $\endgroup$
    – ORN
    Commented Apr 19, 2022 at 9:33
  • $\begingroup$ @YuvalFilmus Can you give me a hint please? $\endgroup$
    – ORN
    Commented Apr 21, 2022 at 13:24
  • $\begingroup$ Consider two cases: $C$ is small and $C$ is large. $\endgroup$ Commented Apr 21, 2022 at 13:52

1 Answer 1


If $|C| < 2^{n/100}$ then $C \not\in \text{CorrectSATSolver}$ since otherwise we would have $\text{SAT} \in \text{Size}(2^{n/100})$.

Assume then that $|C| \ge 2^{n/100}$. Evaluating $C$ for a fixed assignment requires time $|C|$ and there are at most $2^{n}$ possible distinct truth assignments to a formula of size $n$. Therefore $\text{CorrectSATSolver}$ can be decided in time $O(2^{n} \cdot |C|) = O((2^{n/100})^{100} \cdot |C|) \subseteq O(|C|^{101})$ by exhaustively checking the output of $C$ for all possible assignments.


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