From Online Dictionary of Crystallography
Revision as of 14:39, 19 March 2009 by MassimoNespolo (link)
Isomorphisme entre groupes (Fr). Gruppenisomorphismus (Ge). Isomorfismo fra gruppi (It). 同形 (Ja).
A group isomorphism is a special type of group homomorphism. It is a function between two groups that sets up a one-to-one correspondence between the elements of the groups in a way that respects the given group operations. If there exists an isomorphism between two groups, then the groups are called isomorphic. Isomorphic groups have the same properties and the same structure of their multiplication table.
Let (G, *) and (H, #) be two groups, where "*" and "#" are the respective binary operations in G and in H. A group isomorphism from (G, *) to (H, #) is a bijection from G to H, i.e. a bijective function f : G → H such that for all u and v in G it holds that
f (u * v) = f (u) # f (v).
The two groups (G, *) and (H, #) are isomorphic if an isomorphism exists. This is written:
(G, *) [math]\cong[/math] (H, #)
If H = G and # = * then the bijection is an automorphism.