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# the set of [[integers]] <math>\mathbb{Z}</math> under addition: here, zero is the identity, and the inverse of  an element <math>a \in \mathbb{Z}</math> is <math>-a</math>.  
 
# the set of [[integers]] <math>\mathbb{Z}</math> under addition: here, zero is the identity, and the inverse of  an element <math>a \in \mathbb{Z}</math> is <math>-a</math>.  
 
# the set of the positive [[rational number]]s <math>\mathbb{Q}_+</math> under multiplication: <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>.  
 
# the set of the positive [[rational number]]s <math>\mathbb{Q}_+</math> under multiplication: <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>.  
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# the set of complex numbers {1, -1, <i>i</i>,<i>-i</i>} under multiplication, where <i>i</i> is the 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.
 
# 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.
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# the set of complex numbers {1, -1, <i>i</i>,<i>-i</i>} under multiplication, where <i>i</i> is the 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.
      
Groups are the appropriate mathematical structures for any application involving [[symmetry]].
 
Groups are the appropriate mathematical structures for any application involving [[symmetry]].
    
[[Category:Algebra]]
 
[[Category:Algebra]]
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