I need help in another subgroup problem...
please help!
--->Assume that G is a subgroup with operation * and that a E G. Let..
C(a) = { x E G : a *x = x*a}.
prove that C(a) is a subgroup of G?
using the property..
Let G be a group with operation * and let H be a subset of G. Then H is a subgroup of G if and only if:
1) H is non empty.
2) If a E H and b E H then a*b E H
3) If a E H then a(inverse) E H.