Are there some references of the proof of the following result?
Let $(V, c)$ be a braided vector space over a field $k$ with a basis $x_1, \ldots, x_n$, where $c$ is a diagonal braiding given by \begin{align} c(x_i \otimes x_j) = q^{a_{ij}} x_j \otimes x_i, \quad 0 \neq q \in k. \end{align} If $q$ is not algebraic over $\mathbb{Q}$, then the Nichols algebra $B(V)$ is given by \begin{align} k\langle x_1, \ldots, x_n | ad_c(x_i)^{1-a_{ij}}x_j = 0, \ i \neq j \rangle, \end{align} where $ad_c(x_i)(x_j) = x_i x_j - q^{a_{ij}} x_j x_i$.
Thank you very much.
