[OS X TeX] brackets in \aligned

Martin Costabel costabel at wanadoo.fr
Mon Jul 31 09:23:42 EDT 2006

Bruce Kellogg wrote:
> This seems to be a bug. Using version 2.03 I type:
> \begin{equation*}
> \begin{aligned}
> [v](x) &=1, \\
> \{v\}(x) &=1,\\
> [v](x) &=1. \\
> \end{aligned}
> \end{equation*}
> and get 3 displayed equations. The 2nd and 3rd equations are ok,
> but the first equation is:
>   (x) = 1,

Beginning a line with a bracket can give unexpected results if the 
preceding line ends with a command that takes optional arguments. The 
command \begin{aligned} can take an optional placement parameter like 
[t]. In your case it considers [v] as its optional argument and eats it.

To avoid it, place something invisible like {} between the command 
\begin{aligned} and the bracket, or put a % or a real [t] after the 

Actually, you are lucky that your third equation doesn't play you a 
similar trick: The command \\ also takes optional paramters in brackets. 
Apparently the amsmath package paid attention to the definition of \\ so 
that this doesn't happen here.


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