Hey, We can define a group action in two ways: 1) A group G is said to act on a set X, if there exists a group homomorphism ψ : G --> S(X) [the symmetric group of X].
2)Equivalently, a group G acts on a set X, if there is a map from G x X --> X which assigns to each ordered pair <g,x>--->g.x, such that : For all x Є X, e.x = x (h.g).(x) = h.(g.x), where h, g Є G, and x Є X
How are these two definitions equivalent?
Jul 4th 2009, 04:12 PM
Consider the map
For each define by for all Then for all is a bijection from to itself) and the required homomorphism is defined by for all for all