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Using beamer. Let's say I want to write A+B but with the plus invisible in one slide and visible in the next one. I think I read somewhere that more space is left normally around the + for being a binary operator. It seems to be that A\phantom{+}B leaves only the space of the sign +. How can I get all the space I need.

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I don't think the beamer tag is relevant here. – Quinn Culver Sep 23 '11 at 18:17

2 Answers

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Need to add additional {} which emulate a binary operator as TeX thinks there is something on either side of the +:

$A\phantom{{}+{}}B$
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What is the difference between your answer and Stefan's? Is one better? – Quinn Culver Sep 23 '11 at 15:34
@Quinn: AFAIK both add identical spacing around the symbol for a binary operator, but the \mathbin better captures the intent of what you are doing. – Peter Grill Sep 23 '11 at 15:47
When I use &\phanom{=}H... on one line of an align environment and then &=H... on the next, they are misaligned, and using (either of) your trick(s) works. According to your (and Stefan's) explanation, this is because the first = one is not a binary operator whereas the second = is. Am I correct in deducing that the reason the second = is considered a binary operator is because TeX considers the text at the end of the previous line to be to the left of =? – Quinn Culver Sep 23 '11 at 18:16
Not exactly sure I fully understand, perhaps it is best to post an additional question with a full MWE, but using F&\phantom{{}={}}H should produce the proper spacing. – Peter Grill Sep 23 '11 at 18:26
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Use \mathbin for making the invisible symbol a binary operator:

$A\mathbin{\phantom{+}}B$
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What is the difference between your answer and Peter's? Is one better? – Quinn Culver Sep 23 '11 at 15:34
I would think @Stefan's answer is more clear, since you literally define \phantom{+} to act like a binary math operator (via \mathbin. In my opinion, one would only obtain @Peter's solution through experience with this problem, or perhaps a couple of compiles to see whether the spacing is correct. – Werner Sep 25 '11 at 14:33
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@Werner: The spacing will be identical. The {} on either side of the + lets TeX know that there is an item of zero width on either side of the +. But, I do agree that in this case, that \mathbin more clearly captures the intent. – Peter Grill Sep 25 '11 at 22:00
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they may work the same in \phantom, but they dont at the beginning of a line. if i start a line with a logical and, it will attach to the next variable like a unary operator, \mathbin doesnt fix this, {} does. – peter Nov 23 '12 at 10:44

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