What does :=
mean?
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Sign up to join this communityIt is borrowed from computer programming: it means that the item on the left hand side is being defined to be what is on the right hand side. For example, $$y := 7x+2$$ means that $y$ is defined to be $7x+2$.
This is different from, say, writing $$1 = \sin^2(\theta) + \cos^2(\theta)$$ where we are saying that the two sides are equal, but we are not defining "1" to be the expression "$\sin^2(\theta) + \cos^2(\theta)$".
Basically, some people think that there should be notational difference between saying "I define blah
to be equal to blankety
" and saying "blah
is equal to blankety
". So they use :=
for the first and =
for the latter. Usually, it is clear from context which of the two uses of the equal sign is intended (often because of signal words like "Let", "We define", etc.)
=
and ==
nowadays. I have also seen $\leftarrow$ in the context of formal semantics, but hardly ever $:=$.
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:=
for assignment.
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Mar 6, 2011 at 5:02
:=
, but not the others. I think it is possible that the language designers of that time where influenced by maths (as has happened a number of times), but :=
is so far the only easily typable symbol mentioned here, so it is perfectly reasonable to assume it stems from programming languages in the first place. For completeness, I have seen an older TCS-prof (former mathematician) use $=_{df}$ consistently. There might have been an e in there, but not legible.
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I think the Bourbaki used it first.. not sure.. I know physicists use $\equiv$
!=
was chosen because it somehow resembled $\ne$ where !
"strikes through" =
.
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