This paper concerns the open problem of Lovasz and
Saks regarding the relationship between the communication complexity
of a boolean function and the rank of the associated matrix.
We first give an example exhibiting the largest gap known. We then
prove two related theorems.

We present three explicit constructions of hash functions,
which exhibit a trade-off between the size of the family
(and hence the number of random bits needed to generate a member of the family),
and the quality (or error parameter) of the pseudo-random property it
achieves. Unlike previous constructions, ... more >>>

We present a Logspace, many-one reduction from the undirected
st-connectivity problem to its complement. This shows that
$SL=co-SL$

We present a notion of resource-bounded measure for P and other
subexponential-time classes. This generalization is based on Lutz's
notion of measure, but overcomes the limitations that cause Lutz's
definitions to apply only to classes at least as large as E. We
present many of the basic properties of this ... more >>>

The Tutte-Gr\"othendieck polynomial $T(G;x,y)$ of a graph $G$
encodes numerous interesting combinatorial quantities associated
with the graph. Its evaluation in various points in the $(x,y)$
plane give the number of spanning forests of the graph, the number
of its strongly connected orientations, the number of its proper
$k$-colorings, the (all ... more >>>

In this paper we study the pairs $(U,V)$ of disjoint ${\bf NP}$-sets
representable in a theory $T$ of Bounded Arithmetic in the sense that
$T$ proves $U\cap V=\emptyset$. For a large variety of theories $T$
we exhibit a natural disjoint ${\bf NP}$-pair which is complete for the
class of disjoint ... more >>>

We study the computational complexity of languages which have
interactive proofs of logarithmic knowledge complexity. We show that
all such languages can be recognized in ${\cal BPP}^{\cal NP}$. Prior
to this work, for languages with greater-than-zero knowledge
complexity (and specifically, even for knowledge complexity 1) only
trivial computational complexity bounds ... more >>>

Various types of probabilistic proof systems have played
a central role in the development of computer science in the last decade.
In this exposition, we concentrate on three such proof systems ---
interactive proofs, zero-knowledge proofs,
and probabilistic checkable proofs --- stressing the essential
role of randomness in each ... more >>>

We describe a novel randomized method, the method of
{\em color-coding\/} for finding simple paths and cycles of a specified
length $k$, and other small subgraphs, within a given graph $G=(V,E)$.
The randomized algorithms obtained using this method can be
derandomized using families of {\em perfect hash functions\/}. ... more >>>

We introduce the notion of {\em natural} proof.
We argue that the known proofs of lower bounds on the complexity of explicit
Boolean functions in non-monotone models
fall within our definition of natural.
We show based on a hardness assumption
that natural proofs can't prove superpolynomial lower bounds ... more >>>

We consider the fault diagnosis problem: how to use parallel testing
rounds to identify which processors in a set are faulty. We prove
that 4 rounds suffice when 3% or less of the processors are faulty,
and 4 rounds are necessary when any nontrivial constant fraction of
the processors are ... more >>>

It is shown that high order feedforward neural nets of constant depth with piecewise
polynomial activation functions and arbitrary real weights can be simulated for boolean
inputs and outputs by neural nets of a somewhat larger size and depth with heaviside
gates and weights ... more >>>

We introduce a population genetics model in which the operators
are effectively computable -- computable in polynomial time on
Probabilistic Turing Machines. We shall show that in this model
a population can encode easily large amount of information
from enviroment into genetic code. Then it can process the
information as ... more >>>

The modulo $p$ counting principle is a first-order axiom
schema saying that it is possible to count modulo $p$ the number of
elements of the first-order definable subsets of the universe (and of
the finite Cartesian products of the universe with itself) in a
consistent way. It trivially holds on ... more >>>

Suppose that $p$ is a prime number $A$ is a finite set
with $n$ elements
and for each sequence $a=<a_{1},...,a_{k}>$ of length $k$ from the
elements of
$A$, $x_{a}$ is a variable. (We may think that $k$ and $p$ are fixed an
$n$ is sufficiently large.) We will ... more >>>

The modular group occupies a central position in many branches of
mathematical sciences. In this paper we give average polynomial-time
algorithms for the unbounded and bounded membership problems for
finitely generated subgroups of the modular group. The latter result
affirms a conjecture of Gurevich.

It has been known for quite a while that the Vapnik-Chervonenkis dimension
(VC-dimension) of a feedforward neural net with linear threshold gates is at
most O(w log w), where w is the total number of weights in the neural net.
We show in this paper that this bound is in ... more >>>

We prove lower bounds of the form $exp\left(n^{\epsilon_d}\right),$
$\epsilon_d>0,$ on the length of proofs of an explicit sequence of
tautologies, based on the Pigeonhole Principle, in proof systems
using formulas of depth $d,$ for any constant $d.$ This is the
largest lower bound for the strongest proof system, for which ... more >>>

We investigate the computational power of a formal model for networks of
spiking neurons. It is shown that simple operations on phase-differences
between spike-trains provide a very powerful computational tool that can
in principle be used to carry out highly complex computations on a small
network of spiking neurons. We ... more >>>

We consider learning on multi-layer neural nets with piecewise polynomial
activation functions and a fixed number k of numerical inputs. We exhibit
arbitrarily large network architectures for which efficient and provably
successful learning algorithms exist in the rather realistic refinement of
Valiant's model for probably approximately correct learning ("PAC-learning")
where ... more >>>

We review the past ten years in computational complexity theory by
focusing on ten theorems that the author enjoyed the most. We use
each of the theorems as a springboard to discuss work done in
various areas of complexity theory.

We prove that the modular communication complexity of the
undirected graph connectivity problem UCONN equals Theta(n),
in contrast to the well-known Theta(n*log n) bound in the
deterministic case, and to the Omega(n*loglog n) lower bound
in the nondeterministic case, recently proved by ... more >>>

We investigate the computational power of depth two circuits
consisting of $MOD^r$--gates at the bottom and a threshold gate at
the top (for short, threshold--$MOD^r$ circuits) and circuits with
two levels of $MOD$ gates ($MOD^{p}$-$MOD^q$ circuits.) In particular, we
will show the following results

(i) For all prime numbers ... more >>>

We introduce a new method for proving explicit upper bounds on the VC
Dimension of general functional basis networks, and prove as an
application, for the first time, the VC Dimension of analog neural
networks with the sigmoid activation function $\sigma(y)=1/1+e^{-y}$
to ... more >>>

Computing the maximum bichromatic discrepancy is an interesting
theoretical problem with important applications in computational
learning theory, computational geometry and computer graphics.
In this paper we give algorithms to compute the maximum
bichromatic discrepancy for simple geometric ranges, including
rectangles and halfspaces.
In addition, we give ... more >>>

Almost the same types of restricted branching programs (or
binary decision diagrams BDDs) are considered in complexity
theory and in applications like hardware verification. These
models are read-once branching programs (free BDDs) and certain
types of oblivious branching programs (ordered and indexed BDDs
with k layers). The complexity of ... more >>>

A syntactic read-k times branching program has the restriction
that no variable occurs more than k times on any path (whether or not
consistent). We exhibit an explicit Boolean function f which cannot
be computed by nondeterministic syntactic read-k times branching programs
of size less than exp(\sqrt{n}}k^{-2k}), ... more >>>