6. Regression estimation Given two real random variables X and Y admitting a moment of order 2, the (non-linear) regression of Y on X is the function r such that :E(Y−r(X))2≤E(Y−g(X))2, g∈Gwhere G is the family of functions g such that g(X) admits a moment of order 2. So r (X) is the best approximation of Y by a function of X. This is said to be the conditional...