# Disappearing left side of aligned

The following code

\documentclass{amsart}

\begin{document}

\begin{aligned} [E^dx,y]&=E^k[E^{d-k}x,y]-kE^{k-1}[E^{d-k}x,Ey]\\ &+\binom k2E^{k-2}[E^{d-k}x,E^2y]-...\\ &+(-1)^j\binom kjE^{k-j}[E^{d-k}x,E^jy]+...\\ &+(-1)^{k-1}kE[E^{d-k}x,E^{k-1}y]+(-1)^k[E^{d-k}x,E^ky]. \end{aligned}

\end{document}


produces (for me)

As you see, the left-hand side [E^dx,y] of aligned has disappeared.

Does anybody know the reason, and how to prevent it from happening?

• put \relax after \begin{aligned} to stop the [ being taken as an optional argument – David Carlisle Apr 27 at 7:56
• why use \begin{aligned} here rather than \begin{align*} ? – David Carlisle Apr 27 at 7:57 • also help to add \usepackage{mathtools} in preamble of your document. – Zarko Apr 27 at 7:59 • OK if you'd used rather than \[ so the equation number appeared I wouldn't have asked:-) – David Carlisle Apr 27 at 8:02 • doesn't matter really, the issue is just with aligned (we have considered fixing this, but there are some compatibility issues your [E^dx,y] is "clearly" intended to be part of the formula, but if it had been [t] then it may have been intended to specify top alignment and if we change things to make it typeset [t] then documents may break.... – David Carlisle Apr 27 at 8:06 ## 1 Answer This is documented behaviour but not that great and may change in a future release see https://github.com/latex3/latex2e/issues/5 The [...] is taken as an optional argument, so you can "hide" it with \relax \documentclass{amsart} \begin{document} \[ \begin{aligned}\relax [E^dx,y]&=E^k[E^{d-k}x,y]-kE^{k-1}[E^{d-k}x,Ey]\\ &+\binom k2E^{k-2}[E^{d-k}x,E^2y]-...\\ &+(-1)^j\binom kjE^{k-j}[E^{d-k}x,E^jy]+...\\ &+(-1)^{k-1}kE[E^{d-k}x,E^{k-1}y]+(-1)^k[E^{d-k}x,E^ky]. \end{aligned}

\end{document}