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The section [[Function of several real variables#Domain|Domain]] is somewhat questionable... It claims that it might be difficult to specify the ___domain of a function one is defining, which seems backwards. I don't believe that one ''can'' define a function without specifying its ___domain. It is also unreferenced. Can anyone support its claims, or should we remove it? [[User:Siddharthist|siddharthist]] ([[User talk:Siddharthist|talk]]) 21:25, 23 November 2017 (UTC)
:Take any function {{mvar|f}} that has the real line or the complex plane as its ___domain. Knowing the ___domain of {{math|1/''f''}} amounts to know the zeros of {{mvar|f}}, which may be a difficult task. In the case where {{mvar|f}} is [[Riemann zeta function]], to specify the ___domain of {{math|1/''f''}} is equivalent with proving or disproving [[Riemann hypothesis]]. Not an easy task! [[User:D.Lazard|D.Lazard]] ([[User talk:D.Lazard|talk]]) 21:59, 23 November 2017 (UTC)
::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?". 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)
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