diff --git a/Advanced/Symmetric Group/parts/1 cycle.tex b/Advanced/Symmetric Group/parts/1 cycle.tex index 1e438c3..05572e2 100755 --- a/Advanced/Symmetric Group/parts/1 cycle.tex +++ b/Advanced/Symmetric Group/parts/1 cycle.tex @@ -57,14 +57,14 @@ In other words, show that there is always an integer $n$ so that $f^n(x) = x$. \vfill -\definition{Composition} +\definition{Composition} The \textit{composition} of two permutations $f$ and $g$ is the permutation $h(x) = f(g(x))$. \par The usual notation for this is $f \circ g$, but we'll simply write $fg$. \problem{} What is $[1324][4321]$? \par How about $[321][213][231]$? \par -\hint{composition is left-associative, so we evaluate $abc$ as $(ab)c$} +\hint{is composition is left or right-associative? See \ref{compdef}} \vfill @@ -440,7 +440,7 @@ How about $(123)$? And $(4231)$? \par \problem{} -Say $\sigma$ is a permutation composed of cycles $\sigma_1\sigma_2...\sigma_k$. \par +Say $\sigma$ is a permutation composed of disjoint cycles $\sigma_1\sigma_2...\sigma_k$. \par Say we know the order of all $\sigma_i$. What is the order of $\sigma$? \begin{solution} @@ -479,7 +479,8 @@ Show that any permutation is a product of transpositions. Show that any permutation is a product of transpositions of the form $(1, k)$. \par \begin{solution} - Use \ref{simpletrans} and rewrite each $(a, b)$ as $(1, a)(1, b)(1, a)$. + Use \ref{simpletrans} and rewrite each $(a, b)$ as $(1, a)(1, b)(1, a)$. \par + Showing that $(a, b) = (1, a)(1, b)(1, a)$ is fairly easy. \end{solution} \vfill @@ -491,7 +492,8 @@ Show that any permutation is a product of transpositions of the form $(1, k)$. \ Show that any transposition $(a, b)$ is equal to the product $(a, a+1)(a+1, b)(a, a+1)$. \begin{solution} - TODO + This is the same as the $(1, a)(1, b)(1, a)$ case above, but we use $a + 1$ + as a \say{working slot} instead of $1$. \end{solution} \vfill diff --git a/Advanced/Symmetric Group/parts/3 subgroup.tex b/Advanced/Symmetric Group/parts/3 subgroup.tex index 6c9d8d2..b0f4980 100644 --- a/Advanced/Symmetric Group/parts/3 subgroup.tex +++ b/Advanced/Symmetric Group/parts/3 subgroup.tex @@ -98,7 +98,7 @@ Show that $\mathbb{Z}_7^\times$ and $\mathbb{Z}_9^\times$ are isomorphic. \problem{} -Show that $\mathbb{Z}_{10}^\times$ and $\mathbb{Z}_4^\times$, and $\mathbb{Z}_3$ are isomorphic. +Show that $\mathbb{Z}_{10}^\times$ and $\mathbb{Z}_5^\times$, and $\mathbb{Z}_4$ are isomorphic. \hint{ Build a bijection with the above properties. \\ Remember that a group is fully defined by its multiplication table.