Surface operators, dual quivers and contoursS. K. Ashok, S. Ballav, M. Billò, E. Dell’Aquila, M. Frau, V. Gupta, R. R. John and A. LerdaEur. Phys. J. C, 79 3 (2019) 278DOI: https://doi.org/10.1140/epjc/s10052-019-6795-3