22.10. Suppose that c1 and p1 are the prices of a European average price call and a European average price put with strike price K and maturity T, c2 and p2 are the prices of a European average strike call and European average strike put with maturity T, and c3 and p3 are the prices of a regular European call and a regular European put with strike price K and maturity T. Show that c1 + c2 − c3 = p1 + p2 − p3.