EN
Let k be a field of characteristic zero, k[X₁,..., Xₙ] the polynomial ring, and B the ring $k[X₁,..., Xₙ]}/(a₁X₁^{m} + ⋯ + aₘXₙ^{m})$, $0 ≠ a_{i} ∈ k$ for all i and m, n ∈ ℕ with n ≥ 2 and m ≥ 1. Let $Der²_{k}(B)$ be the B-module of all second order k-derivations of B and $der²_{k}(B) = Der¹_{k}(B) + Der¹_{k}(B)Der¹_{k}(B)$ where $Der¹_{k}(B)$ is the B-module of k-derivations of B. If m ≥ 2 we exhibit explicitly a second order derivation $D ∈ Der²_{k}(B)$ such that $D ∉ der²_{k}(B)$ and thus we prove that Nakai's conjecture is true for the k-algebra B.