We prove that it is not decidable on R-machines if for a fixed finite intervall [a,b) the solution of the initial value problems of systems of ordinary differetial equations have solutions over this interval. This result holds independly from assumptions about differentiability of the right sides of the ODEs. Futhermore ... more >>>

A boolean circuit $f(x_1,\ldots,x_n)$ \emph{represents} a graph $G$
on $n$ vertices if for every input vector $a\in\{0,1\}^n$ with
precisely two $1$'s in, say, positions $i$ and $j$, $f(a)=1$
precisely when $i$ and $j$ are adjacent in $G$; on inputs with more
or less than two ... more >>>

In 1977 Valiant proposed a graph theoretical method for proving lower
bounds on algebraic circuits with gates computing linear functions.
He used this method to reduce the problem of proving
lower bounds on circuits with linear gates to to proving lower bounds
on the rigidity of a matrix, a ... more >>>