1. G. ’t Hooft, Magnetic monopoles in unified gauge theories, Nucl. Phys. B 79 (1974) 276 [ INSPIRE ].
2. A.M. Polyakov, Particle spectrum in the Quantum Field Theory, JETP Lett. 20 (1974) 194 [Pisma Zh. Eksp. Teor. Fiz. 20 (1974) 430] [ INSPIRE ].
3. N.S. Manton, A remark on the scattering of BPS monopoles, Phys. Lett. B 110 (1982) 54 [ INSPIRE ].
4. K.G. Wilson, Confinement of quarks, Phys. Rev. D 10 (1974) 2445 [ INSPIRE ].
5. D. Gaiotto, G.W. Moore and A. Neitzke, Framed BPS states, arXiv:1006.0146 [ INSPIRE ].