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::In grade school, an ''extremely common'' [[abuse of language]] is to ask to "find the ___domain of" a given function, which indeed is putting the cart before the horse. What is really meant is "What is the maximal subset of <math>\mathbb{R}^n</math> on which we can use the given expression to define a function?", or even more succinctly, "On what subset of <math>\mathbb{R}^n</math> is this expression defined?". This is probably what is being meant by the statement in question.--[[User:Jasper Deng|Jasper Deng]] [[User talk:Jasper Deng|(talk)]] 22:05, 23 November 2017 (UTC)
: Thank both of you for helping to clarify this point. It seems to me that the expression {{math|1/{{var|f}}}} is not a function ''per se'', but might be if one specified its ___domain, codomain, and arguments correctly. Could someone who has a clearer picture of what this is trying to say rewrite it to actually be ''correct'' (i.e. not abuse language by talking about "functions", but rather "expressions")? Or maybe this is totally clear to most readers and I'm just pedantic :) [[User:Siddharthist|siddharthist]] ([[User talk:Siddharthist|talk]]) 05:47, 24 November 2017 (UTC)
::I may have been too sketchy in my preceding post. In any case, this is not a problem of expressions, this is purely a problem of functions: If {{math|''f''}} is a non-constant continuous function (in the sense of this article, that is, its ___domain contains an open set), then, this is a theorem that <math>\boldsymbol x \to 1/f(\boldsymbol x)</math> is also a function whose ___domain may be difficult to specify, even if {{math|''f''}} and its ___domain are well defined. I have edited the article section for clarifying things (I hope). [[User:D.Lazard|D.Lazard]] ([[User talk:D.Lazard|talk]]) 11:06, 24 November 2017 (UTC)
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