2-semiarcs in $\mathrm{PG}(2,q)$, $q\leq 13$
  A $2$-semiarc is a pointset ${\mathcal S}_k$ with the property that the number of tangent lines to ${\mathcal S}_k$ at each of its points is two. Using some theoretical results and computer aided search, the complete classification of $2$-semiarcs in PG$(2,q)$ is given for $q\leq 7,$ the spectrum of their sizes is determined for $q\leq 9$, and some results about the existence are proven for $q=11$ and $q=13.$ For several sizes of $2$-semiarcs in $\mathrm{PG}(2,q)$, $q\leq 7$, classification results have been obtained by theoretical proofs. 
Daniele Bartoli, Giorgio Faina, Gy\"orgy Kiss, Stefano Marcugini and   Fernanda Pambianco
math.CO