The first part of this thesis strengthens the low-error PCP
characterization of NP, coming closer to the upper limit of the
conjecture of~\cite{BGLR}.

In the second part we show that a boolean function over
$n$ variables can be tested for the property of depending ... more >>>

We show an $\Omega \left(\frac{n^3}{(\ln n)^2}\right)$ lower bound on the size of any depth three ($\SPS$) arithmetic circuit computing an explicit multilinear polynomial in $n$ variables over any field. This improves upon the previously known quadratic lower bound by Shpilka and Wigderson.

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We investigate two QBF resolution systems that use extension variables: weak extended Q-resolution, where the extension variables are quantified at the innermost level, and extended Q-resolution, where the extension variables can be placed inside the quantifier prefix. These systems have been considered previously by Jussila et al. '07 who ... more >>>