I had done some search on this but I was not able to find an answer either way.

Huck answered it fully. Thanks :)

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    $\begingroup$ Can you move your "comment inside the question" to an actual comment. $\endgroup$ Oct 12, 2011 at 22:56
  • $\begingroup$ @Suresh, I do not think there is enough room for it? I am not sure. $\endgroup$
    – Tayfun Pay
    Oct 12, 2011 at 22:59
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    $\begingroup$ Can you perhaps remove the "comment" part entirely? I do not think that it is appropriate. $\endgroup$ Oct 12, 2011 at 23:14
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    $\begingroup$ Put whatever you can and remove the rest. And post this in Huck's answer. It's not appropriate to insert an answer comment inside the original question $\endgroup$ Oct 12, 2011 at 23:29

1 Answer 1


Here's a simple argument that shows that QP is not known to be in PSPACE:

Assume $QP \subseteq PSPACE$. Then we have $P \subsetneq QP \subseteq PSPACE$, where the first inclusion is proper by the time hierarchy theorem.

This separates $P$ from $PSPACE$, which is not known to hold, so $QP \subseteq PSPACE$ must also not be known to hold.

Indeed we have that $PSPACE \subseteq QP \Rightarrow PSPACE \subsetneq EXP$, but $QP \nsubseteq PSPACE$ does not separate the two classes by the THT (as stated in the question).


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