# Phantom width of binary operator

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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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

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
@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
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