The paper by Klebanov and Polyakov explores the AdS/CFT correspondence, focusing on the relationship between theories of infinite higher-spin massless gauge fields in $AdS_{d+1}$ and large $N$ conformal theories in $d$ dimensions. Specifically, they conjecture that the singlet sector of the critical 3-d $O(N)$ model with the $(\phi^a \phi^a)^2$ interaction is dual to the minimal bosonic theory in $AdS_4$ containing massless gauge fields of even spin in the large $N$ limit. The authors discuss the operator structure at large $N$, highlighting the need for composite operators to resolve disconnected contributions in correlation functions. They also propose extensions of the duality to theories with different symmetries and fermionic fields, and suggest a possible generalization to $d=4-\epsilon$. The paper provides a detailed analysis of the operator products and the physical meaning of the dual theories, supporting the conjecture that the AdS/CFT correspondence can be extended to these simpler models.The paper by Klebanov and Polyakov explores the AdS/CFT correspondence, focusing on the relationship between theories of infinite higher-spin massless gauge fields in $AdS_{d+1}$ and large $N$ conformal theories in $d$ dimensions. Specifically, they conjecture that the singlet sector of the critical 3-d $O(N)$ model with the $(\phi^a \phi^a)^2$ interaction is dual to the minimal bosonic theory in $AdS_4$ containing massless gauge fields of even spin in the large $N$ limit. The authors discuss the operator structure at large $N$, highlighting the need for composite operators to resolve disconnected contributions in correlation functions. They also propose extensions of the duality to theories with different symmetries and fermionic fields, and suggest a possible generalization to $d=4-\epsilon$. The paper provides a detailed analysis of the operator products and the physical meaning of the dual theories, supporting the conjecture that the AdS/CFT correspondence can be extended to these simpler models.