# How to have an invisible symbol in an equation for alignment purposes?

Imagine I have a 2-line formula where in the first line I have a probability that I explicitly calculate in the second row, so the second line is much longer, so something like this:

\begin{align*}
& \mathbb P\Big(x\leq 10\Big) \\
&= \mathbb P\Big(x\leq 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1\Big)\\
\end{align*}


If I do that, the probability sign aligns with the = sign, which does not look too good; I would like the two probability signs to align; However, if I do this:

\begin{align*}
& \mathbb P\Big(x\leq 10\Big) \\
= &\mathbb P\Big(x\leq 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1\Big)\\
\end{align*}


I end up with very little space in the second line between the '=' and the probability symbol P; Of course I could add a space, but this seems not no be a very elegant solution; So I thought I add a phantom sign like this

\begin{align*}
&\phantom{=} \mathbb P\Big(x\leq 10\Big) \\
&= \mathbb P\Big(x\leq 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1\Big)\\
\end{align*}


However, this will also not work; So what is the right way to do it?

• Welcome to TeX.SE.
– Mico
Jul 26, 2021 at 2:37

For the formula at hand, the multi-line equation typesetting apparatus of the amsmath package doesn't seem to be all that well suited. I'd therefore just pack most of the material in a \parbox of a suitably chosen width.

\documentclass{article}
\usepackage{amssymb} % for \mathbb macro
\begin{document}
$\mathbb{P}(x\leq 10) \leq\mathbb{P}\bigl(x\leq \parbox[t]{0.7\textwidth}{\raggedright% 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+ 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1 \bigr)}$
\end{document}


I'm dubious about the layout choice here, but the issue with the \phantom attempt was that \phantom{=} will be treated as an ordinary character rather than a relation. If you change it to be \mathrel{\phantom{=}} you will get the alignment you expected.

\begin{align*}
&\mathrel{\phantom{=}} \mathbb P\Big(x\leq 10\Big) \\
&= \mathbb P\Big(x\leq 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1\Big)\\
\end{align*}

• Wouldn't it be much easier to use ={}& in the second line? Jul 26, 2021 at 7:00
• I wrote my answer primarily for those who might come here through search. I'm inclined to think that the whole presentation should be rethought. Jul 26, 2021 at 13:09

What I'd do is to write something like:

\begin{align}
\mathbb P\Big(x\leq 10\Big) & \\
&= \mathbb P
\Big(
x
\le 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1
+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1
\Big)
\end{align}


You want what is before the '=' to be more to the left.

Also consider the tools AMS offers to write split equations, this will end up numbering each line, and I doubt that is what you want.

Or just rewrite, define a variable/function to express your "1+1" ad nauseam as something more manageable (and understandable).

• If you look at the original question a little more closely, you'll see that he used align* and not align. Jul 26, 2021 at 3:31

Another possibilities could be using array adjusting column separation, or alignat in which horizontal space has to be explicitly specified:

\documentclass{article}
\usepackage{amsmath,amssymb}
\setlength{\arraycolsep}{2pt}
\begin{document}
$\begin{array}{rl} &\mathbb P\bigl(x\leq 10\bigr) \\ = & \mathbb P\bigl(x\leq 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1\bigr) \end{array}$

\begin{alignat*}{2}
& \; \mathbb P\bigl(x\leq 10\bigr) \\
= & \; \mathbb P\bigl(x\leq 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1\bigr)
\end{alignat*}
\end{document}


• How would you fix the overfull-line issue in the second row?
– Mico
Jul 26, 2021 at 13:37
• I just didn’t. I was hoping that the equation was just an example of a short row and a long one. To solve it I will add more line breaks, if I want to stick with this methods, the parbox solution you provide it is actually very nice. But as you noted I didn’t take that into account Jul 26, 2021 at 15:57