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Add X as a hypothesis, where X is not known to be either true or false.

3 votes

bounded language complete for NSPACE(log n)?

$\mathsf{L}=\mathsf{NL}$. Yes, there is an analog of Mahaney's Theorem for log-space. If there is a sparse set that is hard for $\mathsf{NL}$ under logspace reductions, then $\mathsf{L}=\mathsf{NL}$: …
Joshua Grochow's user avatar
8 votes
Accepted

Consequence of PIT over $\Bbb Z[x_1,\dots,x_n]$ not having efficient algorithm

Since PIT is in $\mathsf{coRP}$, if there is no efficient derandomization then $\mathsf{P} \neq \mathsf{RP}$ (and, in particular, $\mathsf{P} \neq \mathsf{NP}$, but that's not so surprising, since we …
Joshua Grochow's user avatar
22 votes

Consequences of NP=PSPACE

One point which has been implicitly but not explicitly mentioned yet is that we would get $\mathsf{NP} = \mathsf{coNP}$. Although this is equivalent to $\mathsf{PH}$ collapsing to $\mathsf{NP}$, it fo …
Joshua Grochow's user avatar
27 votes

What would be the consequences of $\mathsf{PH=PSPACE}$?

$\mathsf{PH}$ collapses. A $\mathsf{PSPACE}$-complete problem must be in some level of $\mathsf{PH}$, say it's in $\mathsf{\Sigma_k P}$. Since it's $\mathsf{PSPACE}$-complete$=\mathsf{PH}$-complete (b …
Joshua Grochow's user avatar
8 votes

What specific evidence is there for P = RP?

It's important to note that saying "probabilistic reductions can [probably] be derandomized" is much stronger than P=RP. In fact, one formalization of the notion of derandomizing all randomized reduc …
Joshua Grochow's user avatar
14 votes
Accepted

$\mathsf{EXP}$ vs $\oplus\mathsf{EXP}$

In terms of complexity reasons (rather than complete problems): The Hartmanis-Immerman-Sewelson Theorem should also work in this context, namely: $\mathsf{EXP} \neq \oplus \mathsf{EXP}$ iff there is a …
Joshua Grochow's user avatar
8 votes

What are the consequences of $\mathsf{L}^2 \subseteq \mathsf{P}$?

Group isomorphism (with groups given as multiplication tables) would be in P. Lipton, Snyder, and Zalcstein showed this problem is in $\mathsf{L}^2$, but it is still open whether it is in P. The best …
Joshua Grochow's user avatar
20 votes

Consequences of $NP=coNP$ and $P\ne NP$?

To me, one of the most basic and surprising consequences of $\mathsf{NP}=\mathsf{coNP}$ is the existence of short proofs for a whole host of problems where it is very difficult to see why they should …
Joshua Grochow's user avatar
20 votes

A decision problem which is not known to be in PH but will be in P if P=NP

Answering Scott Aaronson's question, but a bit too long for a comment, here is a construction of a language $L$ such that $P = NP$ implies $L \in P$, but $P \neq NP$ implies $L \notin PH$. Let $M_1, …
Joshua Grochow's user avatar
11 votes

If P = BQP, does this imply that PSPACE (= IP) = AM?

The answers of John Watrous and Andy Drucker are excellent for understanding some of the issues involved. I'll just add to Andy's answer that, not only is no such implication known, but showing such …
Joshua Grochow's user avatar