Incidences between points and lines on a two-dimensional variety

We present a direct and fairly simple proof of the following incidence bound: Let $P$ be a set of $m$ points and $L$ a set of $n$ lines in ${\mathbb{R}}^d$, for $d\ge 3$, which lie in a common algebraic two-dimensional surface of degree $D$ that does not contain any 2-flat, so that no 2-flat contains more than $s \le D$linesof$L$\mathrm{.}Thenthenumberofincidencesbetween$P$and$L$is$$ I(P,L)=O\left(m^{1/2}n^{1/2}D^{1/2} + m^{2/3}\min{n,D^{2}}^{1/3}s^{1/3} + m + n\right). $$When$d=3$, this improves the bound of Guth and Katz~\cite{GK2} for this special case, when $D$ is not too large. A supplementary feature of this work is a review, with detailed proofs, of several basic (and folklore) properties of ruled surfaces in three dimensions.