Before revision:  However, formidable computational requirements of existing approaches often offset these undeniable advantages---particularly in general instrumental variable models with continuous variables .
After revision:  However, formidable computational requirements of existing approaches often offset these undeniable advantages---particularly in general instrumental variable models . However, this flexibility comes at the cost of a ``curse of cardinality'': the number of restrictions on the identified set grows exponentially with the number of points in the support of the endogenous treatment .