The liftability property of weakly relatively compact subsets in M /A ⊥ to M is established for any non-commutative H ∞ -algebra A = H ∞ (M, τ ). Some supplementary results to our previous works are also given.
IntroductionLet H ∞ (D) be the Banach algebra of all bounded analytic functions on the open unit disc D equipped with the supremum norm − ∞ , and it is known that H ∞ (D) is faithfully embedded into L ∞ (T) by taking non-tangential limits. Via the embedding H ∞ (D) has the 'standard' predualhas received much attention in Banach space theory, and indeed many serious investigations were carried out; see, for example, [17; 20, § 6.d]. The present notes are part of our attempts, started in [26], to give more 'functional analysis insight' to many theorems obtained in those investigations on L 1 (T)/H ∞ (D) ⊥ by discussing them in some non-commutative set-up.Natural non-commutative generalizations of H ∞ (D) were introduced by Arveson [4] in the 1960s under the name of maximal subdiagonal algebras, and here we call them noncommutative H ∞ -algebras. The finite tracial ones have been well studied so that we mainly deal with the finite tracial non-commutative H ∞ -algebras in the present notes. Let M be a finite von Neumann algebra with a faithful normal tracial state τ . A σ-weakly closed unital (not necessarily self-adjoint) subalgebra A of M is called a finite tracial non-commutative H ∞ -algebra, which we denote by A = H ∞ (M, τ ), if A + A * is σ-weakly dense in M and the unique τ -preserving conditional expectation E : M → D := A ∩ A * is multiplicative on A. Here we define A * = {a * ∈ M | a ∈ A}, while the symbol X has been used as the dual Banach space of a given Banach space X. The reader can find an excellent survey for non-commutative H ∞ -algebras in [21]. It is plain to see that A has the 'standard' predual M /A ⊥ , which is the main object in our study.It is the main purpose of the present notes to prove that any weakly relatively compact subset in M /A ⊥ can be 'lifted up' to a weakly relatively compact subset in M . In particular, it immediately follows that the Mackey topology on A is indeed the relative topology induced from that on M . Hence, this part of the present notes provides a non-self-adjoint generalization of Sakai's result [24] (also Akemann's result [1, Theorem II.7]). Here, recall that this liftability property was already established by many hands, for example, Kisljakov [14], Delbaen [11] and Pe lczyński [17, § 7], in the 1970s for the classical and commutative L 1 (T)/H ∞ (D) ⊥ and its function algebra generalizations (see [17, p. 54] for further information), and it played a key rôle in any existing proof of the fact that L 1 (T)/H ∞ (D) ⊥ has the Dunford-Pettis