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|  | ==Mathcal== |  | ==Mathcal== | 
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| − | <math>\mathcal{X}</math> | + | <math>X \quad = \quad \langle \mathcal{X} \rangle \quad = \quad \langle u, v \rangle \quad = \quad \{ (u, v) \} \quad \cong \quad \mathbb{B}^2</math> | 
| − |   |  | 
| − | <math>[\mathcal{X}]</math>
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