Can I insert environments like {lgathered} or {gathered}[t] without
resorting to raw TeX? E.g., how would I go about adding the following
into my document?
\begin{align}
x &=
\begin{lgathered}[t]
a + b + c \\
d + e + \begin{gathered}[t]
f + g + h \\
i + j + k
\end{gathered}
\end{lgathered}
\end{align}
Thanks in advance.
