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Group (mathematics)

1 byte added, 19:07, 17 November 2008
Avoids the "positive-ness" issue, and still says what it should. Hooray for words!
# the set of the positive [[rational number]]s <math>\mathbb{Q}_+</math> under multiplication, <math>(\mathbb{Q}_+,\cdot)</math>: <math>1</math> is the identity, while the inverse of an element <math>\frac{m}{n} \in \mathbb{Q}_+</math> is <math>\frac{n}{m}</math>.
# for every <math>n \in \mathbb{N}</math> there exists at least one group with n elements,e.g., <math>(\mathbb{Z}/n\mathbb{Z},+) = (\mathbb{Z}_n,+). </math>
# the set of complex numbers {1, -1, <i>i</i>,<i>-i</i>} under multiplication, where <i>i</i> is the positive principal square root of -1, the basis of the [[imaginary number]]s. This group is [[isomorphism|isomorphic]] to <math> \mathbb{Z}_{4} </math> under mod addition.
# the [[Klein four group]] consists of the set of formal symbols <math>\{1, i, j, k \} </math> with the relations <math> i^{2} =j^{2}=k^{2}=1, \; ij=k, \; jk=i, \; ki=j. </math> All elements of the Klein four group (except the identity 1) have [[order]] 2. The Klein four group is [[isomorphism|isomorphic]] to <math>\mathbb{Z}_{2} \times \mathbb{Z}_{2}</math> under mod addition.