Surface operators, dual quivers and contours S. K. Ashok, S. Ballav, M. Billò, E. Dell’Aquila, M. Frau, V. Gupta, R. R. John and A. Lerda Eur. Phys. J. C, 79 3 (2019) 278 Published online: 26 March 2019 DOI: 10.1140/epjc/s10052-019-6795-3