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==Definition and first consequences==
A function <math>f: \mathbb{R} \rightarrow \mathbb{R}</math> is called a '''
:<math>f(x) = \sum\alpha_i\chi_{A_i}(x)\,</math> for all real numbers <math>x</math>
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==Definition and first consequences==
A function <math>f: \mathbb{R} \rightarrow \mathbb{R}</math> is called a '''
:<math>f(x) = \sum\alpha_i\chi_{A_i}(x)\,</math> for all real numbers <math>x</math>
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