Hörmander staircase
= Hörmander staircase
{c}
Let $P(\xi',z)$ be a polynomial that is monic in the complex variable $z$. A Hörmander staircase partitions the real $\xi'$-space into measurable sets $\Delta_j$ and assigns bounded heights $c_j$ so that $P(\xi',s+ic_j)$ stays uniformly away from zero for $\xi'\in\Delta_j$ and $s\in\mathbb R$. Integrating $1/P$ over the resulting union of horizontal contours constructs a <fundamental solution of a linear differential operator>.