2. X*\Y* 嗰part你可能get錯左D野, 佢唔係將X* restrict落Y*到, 佢意思係for x* in X*, 即係bounded linear functional on X , 如果restrict個domain落Y到係bounded linear functional on Y. 所以個restriction induced a well defined map from X* -> Y*. 而你個zeta係eta composite 呢個inclusion map, 所以define到. 同埋 X*其實係subspace of Y*