I just read Azov's article in the considered two classes of Riemannian metrics, \begin{align*} ds^2&=du_1^2+f(u_1)\sum_{i=2}^ldu_i,&f>0\\ ds^2&=g^2(u_1)\sum_{i=2}^ldu_i^2 ,&g>0\end{align*} and solved the problem of their immersibility into $\mathbb R^n$ and $\mathbb S^n$, $n>l$. He proves the following theorems
- The metrics admit isometric immersions into the Euclidean space $\mathbb R^{4l-3}$.
- The metrics admit isometric immersions into the Euclidean space $\mathbb S^{4l-3}$.
But in Surfaces of Negative Curvature of Rozendorn, he mentions the following I can't understand how Rozendorn comes to that conclusion, can someone help me? On the other hand, is there already an improvement for that lower bound for isometric immersions?
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