In [1], [2] HOÀNG TUY gave an approach to the main theorems of the convex analysis and the convex optimization being based on a lemma; he has proved it by means o induction. In [1] the equivalence of the main theorems of convex optimization given in [1], [2] does not use a separation theorem or equivalent statements. In this note the author has proved that the lemma of HOÀNG TUY can be characterized as a special separation theorem and be obtained from a separation theorem of Eidelheit. That means that the lemma is equivalent to the theorem of Hahn-Banach.