THE NORMING SETS OF L(² l²₁) and L_s (² l³₁)

Let n ∈ N. An element (x₁, …, x_n) ∈ Eⁿ is called a norming point of T ∈ L(ⁿ E) if ∥x₁ ∥ = · · · = ∥x_n ∥ = 1 and |T (x₁, …, x_n)| = ∥T ∥, where L(ⁿ E) denotes the space of all continuous n-linear forms on E. For T ∈ L(ⁿ E), we define Norm(T) = { (x₁, …, x_n) ∈ Eⁿ: (x₁, …, x_n) is a norming point of T } . Norm(T) is called the norming set of T . We classify Norm(T) for every T ∈ L(² l1)² or L_s (² l1),³ where l1ⁿ = Rⁿ with the l₁-norm.