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A subgroup H of finite index in a group G (finite or infinite) always contains a normal subgroup N (of G), also of finite index. In fact, if H has index n, then the index of N will be some divisor of n! and a multiple of n; indeed, N can be taken to be the kernel of the natural homomorphism from G to the permutation group of the left (or right ...
The identity of a subgroup is the identity of the group: if G is a group with identity e G, and H is a subgroup of G with identity e H, then e H = e G. The inverse of an element in a subgroup is the inverse of the element in the group: if H is a subgroup of a group G, and a and b are elements of H such that ab = ba = e H, then ab = ba = e G.
In group theory, a word is any written product of group elements and their inverses. For example, if x, y and z are elements of a group G, then xy, z −1 xzz and y −1 zxx −1 yz −1 are words in the set {x, y, z}. Two different words may evaluate to the same value in G, [1] or even in every group. [2]
The second method is used when the number of elements in each row is the same and known at the time the program is written. The programmer declares the array to have, say, three columns by writing e.g. elementtype tablename[][3];. One then refers to a particular element of the array by writing tablename[first index][second index]. The compiler ...
If G is any group, and S is a generating subset of G, then every element of G is also of the above form; but in general, these products will not uniquely describe an element of G. For example, the dihedral group D 8 of order sixteen can be generated by a rotation, r , of order 8; and a flip, f , of order 2; and certainly any element of D 8 is a ...
For n > 1, the group A n is the commutator subgroup of the symmetric group S n with index 2 and has therefore n!/2 elements. It is the kernel of the signature group homomorphism sgn : S n → {1, −1} explained under symmetric group. The group A n is abelian if and only if n ≤ 3 and simple if and only if n = 3 or n ≥ 5.
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However, many readers find this confusing, as the indentation makes it look more like a continuation of the last sublist item. Also, this technique may give, depending on CSS, a blank line before and after each list, in which case, for uniformity, every first-level list item could be made a separate list although this further complicates the code.