Association of Random Variables, with Applications

Ann. Math. Statist. 38(5):1466-1474. Defines association through nonnegative covariance of coordinatewise nondecreasing transforms and proves closure properties. Historical source for the covariance-sign language only; Jakubowski 2021, not this paper or FKG, is the direct equality-case source consumed by the DS17 conditional Chebyshev step.