Structure of total subspaces of dual Banach spaces

Let $X$ be a separable nonquasireflexive Banach space. Let $Y$ be a Banach space isomorphic to a subspace of $X^*$. The paper is devoted to the following questions: 1. Under what conditions does there exist an isomorphic embedding $T:Y\to X^*$ such that subspace $T(Y)\subset X^*$ is total? 2. If such embeddings exist, what are the possible orders of $T(Y)$? Here we need to recall some definitions. For a subset $M\subset X^*$ we denote the set of all limits of weak$^*$ convergent sequences in $M$ by $M_{(1)}$. Inductively, for ordinal number $α$ we let $M_{(α)}=\cup_{β<α}(M_{(β)})_{(1)}.$ The least ordinal $α$ for which $M_{(α)}= M_{(α+1)}$ is called the {\it order} of $M$.

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