(Restricted Least Squares) Show that the restricted least-squares program (4.2) is equivalent to subject to $$K = r$$ when rank(X) = K and Assumption 7.1

(Restricted Least Squares) Show that the restricted least-squares program (4.2) is equivalent to

subject to $$Kβ = r$$
when rank(X) = K and Assumption 7.1

(Second Moments, p. 130) holds.

min(-8) Var[|X]' (B-B) subject to K=r B