Dihedral coverings of trigonal curves Alex Degtyarev 14H3014H4514H50trigonal curvefundamental groupdihedral coveringmodular group We classify and study trigonal curves in Hirzebruch surfaces admitting dihedral Galois coverings. As a consequence, we obtain certain restrictions on the fundamental group of a plane curve $D$ with a singular point of multiplicity $(\deg D-3)$. Indiana University Mathematics Journal 2012 text pdf 10.1512/iumj.2012.61.4607 10.1512/iumj.2012.61.4607 en Indiana Univ. Math. J. 61 (2012) 901 - 938 state-of-the-art mathematics http://iumj.org/access/