i) is the set of self inverse elements of .
I need to show that is a subgroup of if is abelian.
SG1 = Since neutral element is its self inverse, H is not empty
SG2 = a*b member of H, for all a,b member of H
since f is abelian
Hence it satisfies conditon of H
SG3 = every element is its self inverse
Thus member of H