In § 4 , we consider vectorlike ( " QCD - like " ) gauge theories . In § 4.1 , we study in some detail the infrared theory of an SU(3 ) gauge theory with one sextet - representation Dirac fermion , as it has not been previously considered in the literature ( this theory is confining ) . In § 4.2 , we give our results for the conformal window for SU(N ) vectorlike theories with N D f two - index symmetric Dirac fermions . In § 4 . Comparison of our results for the conformal window with those of other analytic approaches are given in § 6 . We begin , in § 6.1 , by giving comparisons of our approach with the truncated Schwinger - Dyson equations and supersymmetry - inspired estimates , see Tables 3 , 4 , 5 , 6 . In § 6.2 , we compare some features of the various approaches . In § 6.3 , we compare with the available lattice data .