# [OS X TeX] Latex symbol for "define equal"

juan tolosa juantolo at me.com
Tue Aug 21 23:08:50 CEST 2018

```I will limit myself to answer your question, since this discussion belongs somewhere else:
VERY simple: Write “Definition” before the statement, or “Theorem”, depending on what you mean.

> On Aug 21, 2018, at 7:02 AM, Markus Klyver <markusklyver at hotmail.com> wrote:
>
> But how would the reader know if it's a theorem or a definition? Consider the statement "f(x)=1 when x=2". Do we mean f(x)=1 <---> x=2 or just f(x)=1 <--- x=2?
>
>
> Från: MacOSX-TeX <macosx-tex-bounces at email.esm.psu.edu <mailto:macosx-tex-bounces at email.esm.psu.edu>> för Josep Maria Font <jmfont at ub.edu <mailto:jmfont at ub.edu>>
> Skickat: den 21 augusti 2018 12:15
> Till: TeX on Mac OS X Mailing List
> Ämne: Re: [OS X TeX] Latex symbol for "define equal"
>
> That's why I prefer to use "when" for definitions: [...this NEW thing happens...] WHEN [...such-and-such known, understandable condition holds...].
>
>
> JMaF
>
>
> > El 21 /08/18, a les 5:40, juan tolosa <juantolo at me.com> va escriure:
> >
> > This is tangential but, since we are at it, what really, really annoys me, is the tendency in some books to define concepts using “if and only if” instead of plain “if”, as in
> >
> > Definition. A sequence (a_n) converges to a real number p if and only if for every epsilon > 0 there is an N such that (etc.)
> >
> > (Is it my impression, or there is a growing number of such texts? And when did this nonsense begin?)
> >
> > One could simply agree that the “if” in definitions is not the same as the “if” in logical statements.
> > If one is really fastidious, one could put a statement at the beginning of the book that “if” in definitions can be reworded as, say,
> > by “(a_n) converges to p” we mean … (etc)
> > Or simply not use “if” at all in definitions.
> > What is even more annoying is that when the definition gets really involved, the “if and only if” makes it even worse.
> > And, invariably, in a really involved definition you will find that the author(s) abandon their own fastidiousness and just use “if.”
> > Question is, why not do it from the very beginning?
> >
> > Juan
> >
> >> On Aug 20, 2018, at 7:56 PM, Markus Klyver <markusklyver at hotmail.com> wrote:
> >>
> >> Really, there's no standardized notation for it. Just be consistent and use the most aesthetically pleasing and practical notation on your context. Maybe := looks ugly will your fonts. Use an other notation instead.
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