1. The problem statement, all variables and given/known data Here's the question: http://assets.openstudy.com/updates...3c487dfb-ceb105-1360099849081-grouptheory.png 2. Relevant equations 3. The attempt at a solution Step 1: <S,T> subset <<S>,T> subset <<S>,<T>> (easy) and Step 2: <S,T> subset <S,<T>> subset <<S>,<T>> (easy) and Step 3: <<S>,<T>> subset <S,T> (slightly trickier) I've done step 1 and 2 by saying <S> is smallest subgroup of G containing all elements of S and similarly with T. No idea how to do step 3 i.e. how to show <<S>,<T>> subset <S,T> ??