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I would like to uncover a set of equations line by line with and the covered equations should be transparent. The problem occurs when I want to align those equations: somehow the transparency stops at the &-sign.

I attached a minimum working example of the problem, where you can see that only the arrow is transparent instead of the whole line.

I've read the beamer User's Guide but I couldn't find any detailed information about the \uncover-command and known complications, but maybe somebody here is able to help me.

I appreciate any help.






        \uncover<1->{& a = b \wedge b = c \\}
        \uncover<2->{\Rightarrow & a = c \\}

share|improve this question
Welcome to TeX.sx! It's not necessary to sign your questions (as there is already a box with your username below it) or to begin them with a greeting. – Werner Nov 23 '11 at 23:27
I know, it's not necessary, but I'm accostumed to greet when I start new thread and I regard it as polite. – Dave Nov 24 '11 at 18:57
That's fine too, but this Q&A is accustomed to be question-specific. As such, many users with the edit privilege will remove these greetings and signatures. – Werner Nov 24 '11 at 19:00
up vote 2 down vote accepted

Read chapter 23.4 of the beamer guide ("23.4 Uncovering Tagged Formulas Piecewise").

Notice: this is not an RTFM answer, this is easy to miss.

Edit: as egreg noticed, the above "answer" does not actually answer the question...

Now this is ugly, but works:




      \uncover<1->{a = b \wedge b = c \\}
      \uncover<2->{\mathrlap{\Rightarrow a = c}\hphantom{a = b \wedge b = c}\\}


(It does at the expense of manually specifying the longest line, and doing it twice. A hackery, non-LaTeX-style, ugly "solution", but hey, the pdf looks good.)

Also, one could imagine semi-automating it to something like this:



\newcommand{\longest}[1]{\sbox{\longestlinebox}{$\displaystyle #1$}\longestalignlinelength=\wd\longestlinebox}


  \longest{a = b \wedge b = c}
    \uncover<1->{\putline{a = b \wedge b = c}\\}
    \uncover<2->{\putline{\Rightarrow a = c}\\}


Still not very elegant, but a bit better.

share|improve this answer
The manual says precisely to do what Dave is doing; but it doesn't work with transparent, while it does with invisible. – egreg Nov 23 '11 at 23:38
Ooops, sorry, then. – mbork Nov 23 '11 at 23:49
I've put something closer to an answer now. – mbork Nov 24 '11 at 0:07
Thanks for the manual and automatic solutions. Works great. – Dave Nov 24 '11 at 18:56
You're welcome:). Notice that this will only work if all the "equations" are to be aligned left; if you want to align them at the equals sign or something like that, you'd have to modify this solution accordingly. – mbork Nov 24 '11 at 21:39

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