State the van Kampen theorem for fundamental groups. Use it to compute,
\(\pi _1(K,*)\), where \(K\) is the Klein bottle, and \(\pi _1(S_g,*)\), where \(S_g\) is the orientable surface of genus
\(g\). (Here \(*\) is any base-point.)
Show that \(S_g\) is indeed orientable; carefully state the results you are using.