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How do I write in the right way, that something is constant?

I think, usually one does write = const., which should be an abbreviation for the Latin constat.

Should I write the expression italic ($\textit{const.}$) or upright ($\textrm{const.}$)? As far as I know, fixed mathematical operators should be written upright, but this isn't an operator...

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    $\begingroup$ As I understand it, the rule is really that anything that is part of an actual word (rather than just the name of a variable) should be upright. Of course, the best thing to do is to search through some well-produced books and see if you can see how they do it. $\endgroup$
    – Schemer
    Jul 13, 2015 at 19:07
  • $\begingroup$ Would this question not be better posed on tex.stackexchange? $\endgroup$
    – Zain Patel
    Jul 13, 2015 at 19:22
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    $\begingroup$ @ZainPatel I wasn't sure. But it's also not an actual Tex/Latex question... $\endgroup$
    – user254303
    Jul 13, 2015 at 19:26

3 Answers 3

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Formally speaking, the right way to doing it would be to write something like $$\int 2x\, \mathrm{d}x = x^2 + k, \ \text{where } k \text{ is constant}$$ If you did insist on doing it that way, to me it would look weird if it was italicised: italicised letters inside equations or formulae are usually interpreted as variables, so you technically end up with some ambiguity if any of the letters $c,o,n,s,t$ are used as variables. So I'd certainly prefer $$\int 2x\, \mathrm{d}x = x^2 + \text{const.}$$ ...but, of course, there is no Mathematical Institute of the Universe to govern this kind of thing, so as they say on Jersey Shore, you do you.

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I have seen it written in both ways, and reckon it is more a matter of taste. Most frequently I have seen it in italics written as

$$ \cdots = const. $$ This makes sense, I guess that fromo context it would be very difficult to confuse it with some other mathematical expression, such as the product of $c,o,n,s,t$.

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    $\begingroup$ The reason could of course just be that if you just type const. without any further commands in $\rm\LaTeX$ formulas, you get italics. $\endgroup$
    – celtschk
    Jul 13, 2015 at 19:21
  • $\begingroup$ Good point you are making, that is likely. $\endgroup$ Jul 13, 2015 at 19:24
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I believe your question has a definite answer if you fix a particular formal language, e.g. the language of first-order logic, in which you express a well-formed formula.

You could specify a constant symbol from the signature of the language to address a particular term in the domain of discourse. You could use quantifiers (if those exist in your language) to express a more complex association of an expression with a fixed member of the domain.

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  • $\begingroup$ Oops, miss read the question. $\endgroup$
    – mcg256
    Jul 14, 2015 at 1:19

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