“…In this case the free energy is a function of the R charge, and the properties of the N = 2 theories require the knowledge of the exact R charge current appearing in the superconformal algebra. Surprisingly, as first observed in [5], the exact R charges have the special property of extremizing the free energy F. 1 In every known example this extremization is a maximization, and identifying the free energy as a good candidate for counting the number of degrees of freedom led to conjecture a three-dimensional c-theorem, known as F-theorem [7][8][9]. In [8,10], the F-maximization was found to be valid along the whole RG flows of a large class of weakly coupled theories, even without supersymmetry [8], corroborating the validity of an F-theorem.…”