88 CHAPTER 2. REPRESENTATIONS OF THE SYMMETRIC GROUP
8. Verify that the permutations \(\pi\) chosen after Definition 2.6.1 do indeed
form a transversal for \(S_A \times S_B\) in \(S_{A \cup B}\).
9. Verify the statements made in case 2 for the computation of Young's
natural representation (page 74).
10. In \(S_n\) consider the transpositions \(\tau_k = (k, k + 1)\) for \(k = 1, \dots, n - 1\).
(a) Prove that the \(\tau_k\) generate \(S_n\) subject to the Coxeter relations
\(\tau_k^2 = \epsilon,\)
\(1 \le k \le n - 1,\)
\(\tau_k \tau_{k+1} \tau_k = \tau_{k+1} \tau_k \tau_{k+1},\)
\(1 \le k \le n - 2,\)
\(\tau_k \tau_l = \tau_l \tau_k,\)
\(1 \le k, l \le n - 1 \text{ and } |k - l| \ge 2.\)
(b) Show that if \(G_n\) is a group generated by \(g_k\) for \(k = 1, \dots, n - 1\)
subject to the relations above (replacing \(\tau_k\) by \(g_k\)), then \(G_n \cong S_n\). Hint: Induct on \(n\) using cosets of the subgroup generated by
\(g_1, \dots, g_{n-2}\).