MyWikiBiz, Author Your Legacy — Saturday November 23, 2024
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, 00:45, 13 February 2013
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| | <math>\prod_{i=1}^n X_i ~=~ X_1 \times \ldots \times X_n ~=~ \{ (x_1, \ldots, x_n) : x_i \in X_i \}.\!</math> | | | <math>\prod_{i=1}^n X_i ~=~ X_1 \times \ldots \times X_n ~=~ \{ (x_1, \ldots, x_n) : x_i \in X_i \}.\!</math> |
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| + | As an alternative definition, the <math>n\!</math>-tuples of <math>\prod_{i=1}^n X_i\!</math> can be regarded as sequences of elements from the successive <math>X_i\!</math> and thus as functions that map <math>[n]\!</math> into the sum of the <math>X_i,\!</math> namely, as the functions <math>f : [n] \to \bigcup_{i=1}^n X_i\!</math> that obey the condition <math>f(i) \in i \widehat{~} X_i.\!</math> |
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| <pre> | | <pre> |
− | As an alternative definition, the n tuples of Xi Xi can be regarded as sequences of elements that come from the successive Xi, and thus as the various functions of a certain sort that map [n] into the sum of the Xi, namely, as the sort of functions f : [n] > Ui Xi that obey the condition f(i) C i^Xi.
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| Xi Xi = X1 x ... x Xn = { f : [n] > Ui Xi | f(i) C Xi for all i}. | | Xi Xi = X1 x ... x Xn = { f : [n] > Ui Xi | f(i) C Xi for all i}. |
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