A *linear hypergraph* is a pair $\pi=(V, L)$ where $V\neq \emptyset$ is a set and $L\subseteq {\cal P}(V)$ has the following properties:

 1. for $e\in L$ we have $|e|\geq 2$;
 2. if $e_1\neq e_2 \in L$ then $|e_1\cap e_2|\leq 1$.

We set $V(\pi)=V$ and $L(\pi)=L$. The *graph* $G_\pi$ *associated to* a linear hypergraph $\pi$ is given by $G=(V,E)$ where $V = L$ and $E = \{\{e_1, e_2\} \subseteq L: e_1\neq e_2\text{ and } e_1\cap e_2\neq \emptyset\}$. It turns out that for any graph $G$ there is a linear hypergraph $\pi$ such that $G\cong G_\pi$. For any graph $G$ the we set $$\ell(G) := \text{min}\{|V(\pi)|:\pi \text{ is a linear hypergraph such that } G_{\pi} \cong G\}$$ and call this the *linear intersection number* of $G$. (For infinite graphs, this concept is boring: $\ell(G) = |V(G)|$ for infinite graphs.)

For any graph $G=(V,E)$ let $\tau(G)$ be the minimum cardinality of a [vertex cover][1] of $G$. 

Does $\tau(G) \leq \ell(G)$ hold for all graphs $G$?

  [1]: http://en.wikipedia.org/wiki/Vertex_cover