Norm-peak multilinear forms on l1

Let n ∈ N, n≥ 2. A continuous n-linear form T on a Banach space E is called norm-peak if there is unique (x1, . . . , xn) ∈ En such that ∥x1∥ = ··· = ∥xn∥ = 1 and T attains its norm only at (±x1,...,±xn). In this paper, we characterize the norm-peak multilinear forms on l1.