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I have several long formulae, each formula occupies almost the whole width of the line:

$$ 1 * 2 + 3 * 4 + 5 * 6 + ( 7 * 8 ) \tag{a}$$ $$= 1 * 2 + 3 * 4 + 5 * 6 + 7 * 8 \tag{b}$$ $$<> 1 * 2 + 3 * 4 + 5 * ( 6 + 7 ) * 8 \tag{c}$$

Then I would like to add "$b <> $e" and "$e = f$":

$$ 1 * 2 + 3 * 4 + 5 * 6 + 7 * 8 \tag{b}$$ $$<> 1 * 2 + 3 * ( 4 + 5 ) * 6 + 7 * 8 \tag{e}$$ $$= 1 * 2 + 3 * 9 * 6 + 7 * 8 \tag{f}$$

But here I have repeated $(b)$... Does anyone have an idea to represent all these relations without repeating any formula?

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I don't understand what you're trying to do. Can you give an example of formulas that you are trying to add, and add them? –  mixedmath Mar 3 '12 at 20:10
    
Is it better now? –  SoftTimur Mar 3 '12 at 20:36
    
what does $<>$ mean? Did you want to use $\neq$ (i.e. not equal)? –  Aryabhata Mar 5 '12 at 1:25
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Are you worried about repeating a formula, or repeating a letter that stands for a formula? If you aren't worried about repeating a letter, you could just say, "Let $a=\dots,b=\dots$, etc., and then write $a=b,b\ne c, b\ne e,e=f$. Each formula gets written only once, but the letters standing for the formulas get written more than once.

If you don't even want to write any letter twice, the problem is that $b$ is involved in three relations ($a=b$, $b\ne c$, and $b\ne e$), so any linear string of symbols giving all your relations will have to use $b$ more than once. If you're willing to go to two dimensions, you could have points labelled $a,b,c,e,f$ and one kind of line between two points for equality and a different kind for inequality - say, a straight line and a wavy line, or a red line and a blue line. or a line with an equals sign on it and a line with a not-equals sign on it. Of course you'd have to explain the notation to anyone who is going to read what you've written.

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