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Let $k$ be a field. Let $X$ be a subvariety of $\mathbb P_k^r$ of dimension $n$. If $k$ is an algebraically closed field of characteristic $0$, then

(1). If $r \le 2n - 1$, then $X$ is simply connected ($X$ has trivial étale fundamental group).

(2). If $r \le 2n - 2$, then $\mathop{\mathrm{Pic}}(X) \cong \mathbb Z$.

If $k = \mathbb C$, then we can prove these statements using Barth's theorem, the general cases can be prove by reducing to $\mathbb C$. I wonder if there is an algebraic proof of the general case.

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  • $\begingroup$ Have you looked at papers of Ogus? $\endgroup$
    – Mohan
    Dec 10, 2020 at 19:02
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    $\begingroup$ (1) is proved in Fulton-Hansen, Ann. of Math. (2) 110 (1979), no. 1, 159-166. This is Corollary 2 on the first page. $\endgroup$
    – abx
    Dec 10, 2020 at 21:12

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