Given any group G and a subset W, let < W > be the smallest subgroup of G which contains W?

A) prove that there is such a subgroup < W > in G. ( < W > is called the subgroup generated by W.)

B) If gwg ^ -1 € W for all g € G, w € W, prove that < W > is a normal subgroup of G.

C) Now, let U={xyx^ -1y^-1 | x, y € G}. Prove that < U > is normal in G.