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Stufe (=level) of a non-real field (wikipedia.de). It is the least number of squares $a_i^2$ such that $\sum_i a_i^2 = -1$, $\infty$ if no such sum exists.

In this paper, the level of a subgroup of $SL_2(\mathcal{O})$ is defined ($\mathcal{O}$ a number field), as the generalisation of the stufe of a field, so the term has been translated, but only in a shift of context.

To pick a random paper, try The stufe of number fields.

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Stufe (=level) of a non-real field (wikipedia.de). It is the least number of squares $a_i^2$ such that $\sum_i a_i^2 = -to 1$, $\infty$ if no such sum exists.

To pick a random paper, try The stufe of number fields.