We show that there are infinitely many primes $p$, such
that the subgroup membership problem for PSL(2,p) belongs
to $\NP \cap \coNP$.

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We investigate the computational complexity
of the minimal polynomial of an integer matrix.

We show that the computation of the minimal polynomial
is in AC^0(GapL), the AC^0-closure of the logspace
counting class GapL, which is contained in NC^2.
Our main result is that the problem is hard ... more >>>

We present a weaker variant of the PCP Theorem that admits a
significantly easier proof. In this
variant the prover only has $n^t$ time to compute each
bit of his answer, for an arbitray but fixed constant
$t$, in contrast to
being all powerful. We show that
3SAT ... more >>>