eans}
&amp;= \overline{Y_T} - \overline{Y_U} \\
&amp;= \overline{Y_T^1} - \overline{Y_U^0}
\end{aligned}$$`

--

Next, I'll use an algebraic trick -- add and subtract the same term:
`$$\begin{aligned}
\text{Difference in Means}
&amp;= \overline{Y_T^1} - \overline{Y_U^0} + 0\\
&amp;= \overline{Y_T^1} - \overline{Y_U^0} + \Big( \overline{Y_T^0} - \overline{Y_T^0} \Big)
\end{aligned}$$`

--

Rearranging, we get:
`$$\text{Difference in Means} = \underbrace{
  \Big(\overline{Y_T^1} - \overline{Y_T^0}\Big)
  }_\t