Lemma 55.4.2. Let n, m_ i, a_{ij}, w_ i, g_ i be a numerical type T. The Picard group of T is a finitely generated abelian group of rank 1.
Proof. If n = 1, then A = (a_{ij}) is the zero matrix and the result is clear. For n > 1 the matrix A has rank n - 1 by either Lemma 55.2.2 or Lemma 55.2.3. Of course the rank is not affected by scaling the rows by 1/w_ i. This proves the lemma. \square
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