EN
Let $𝓐_{∞}(B_{X})$ be the Banach space of all bounded and continuous functions on the closed unit ball $B_{X}$ of a complex Banach space X and holomorphic on the open unit ball, with sup norm, and let $𝓐_{u}(B_{X})$ be the subspace of $𝓐_{∞}(B_{X})$ of those functions which are uniformly continuous on $B_{X}$. A subset $B ⊂ B_{X}$ is a boundary for $𝓐_{∞}(B_{X})$ if $∥f∥ = sup_{x∈ B} |f(x)|$ for every $f ∈ 𝓐_{∞}(B_{X})$. We prove that for X = d(w,1) (the Lorentz sequence space) and X = C₁(H), the trace class operators, there is a minimal closed boundary for $𝓐_{∞}(B_{X})$. On the other hand, for X = 𝓢, the Schreier space, and $X = K(ℓ_{p},ℓ_{q})$ (1 ≤ p ≤ q < ∞), there is no minimal closed boundary for the corresponding spaces of holomorphic functions.