ISO 31-11

ISO 31-11 was the part of international standard ISO 31 that defines mathematical signs and symbols for use in physical sciences and technology. It was superseded in 2009 by ISO 80000-2.

Its definitions include the following:

ℤ^* = ℤ ∖ {0} = {..., −3, −2, −1, 1, 2, 3, ...}

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