# The Unapologetic Mathematician

## Young Tabloids

Close cousins to Young tableaux, Young tabloids give us another set on which our symmetric group will act.

We say that two Young tableaux are “row-equivalent” if they contain the same entries in the same rows. That is, if we start with a Young tableau and shuffle the entries in each row — but never send an entry from one row to another row — then the resulting tableau is row-equivalent to the one we started with. Any two row-equivalent tableaux are related in this way.

We define a Young tabloid to be a row-equivalence class of Young tableaux, and we write it by writing down any tableau in the class, but with horizontal bars through it. As an example, there are three Young tabloids of shape $(2,1)$:

\displaystyle\begin{aligned}\begin{array}{cc}\cline{1-2}1&2\\\cline{1-2}3&\\\cline{1-1}\end{array}&=\left\{\begin{array}{cc}1&2\\3&\end{array},\begin{array}{cc}2&1\\3&\end{array}\right\}\\\begin{array}{cc}\cline{1-2}1&3\\\cline{1-2}2&\\\cline{1-1}\end{array}&=\left\{\begin{array}{cc}1&3\\2&\end{array},\begin{array}{cc}3&1\\2&\end{array}\right\}\\\begin{array}{cc}\cline{1-2}2&3\\\cline{1-2}1&\\\cline{1-1}\end{array}&=\left\{\begin{array}{cc}2&3\\1&\end{array},\begin{array}{cc}3&2\\1&\end{array}\right\}\end{aligned}

If we have written the tableau abstractly as $t$, then the corresponding tabloid is $\{t\}$ — the equivalence class of $t$.

December 11, 2010