1. T. Schäfer and E.V. Shuryak, Instantons in QCD, Rev. Mod. Phys. 70 (1998) 323 [ hep-ph/9610451 ] [ INSPIRE ].
2. D. Diakonov, Chiral symmetry breaking by instantons, Proc. Int. Sch. Phys. Fermi 130 (1996) 397 [ hep-ph/9602375 ] [ INSPIRE ].
3. A.M. Polyakov, Quark Confinement and Topology of Gauge Groups, Nucl. Phys. B 120 (1977) 429 [ INSPIRE ].
4. S. Vandoren and P. van Nieuwenhuizen, Lectures on instantons, arXiv:0802.1862 [ INSPIRE ].
5. C. Bonati and M. D’Elia, Comparison of the gradient flow with cooling in SU(3) pure gauge theory, Phys. Rev. D 89 (2014) 105005 [ arXiv:1401.2441 ] [ INSPIRE ].