Before revision:  Our formulation circumvents the first-stage regression which can be a bottleneck in modern two-stage procedures for IV regression. We also show that our framework is closely related to the generalized method of moments (GMM) with specific assumptions. This highlights the fundamental connection between GMM and two-stage procedures in IV literature. Using the proposed framework , we develop a simple kernel-based algorithm with consistency guarantees.
After revision:  Our formulation circumvents the first-stage regression which is a potential bottleneck in real-world applications. Based on this new approach , we develop a simple kernel-based algorithm with consistency guarantees.