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data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> </div> <div id="contentSub"><div id="mw-content-subtitle">← <a href="/wiki/Bijektiv" title="Bijektiv">Bijektiv</a></div></div> <div id="mw-content-text" class="mw-body-content"><p>Du har ikke rettigheder til at redigere denne side af følgende grund: </p> <div class="permissions-errors"><div class="mw-permissionerror-globalblocking-blockedtext-range"><b>Din IP-adresse er inden for et interval blevet <a href="https://meta.wikimedia.org/wiki/Special:MyLanguage/Global_blocks" class="extiw" title="m:Special:MyLanguage/Global blocks">blokeret på alle Wikimedia Foundation-wikier</a>.</b> <p>Blokeringen blev foretaget af <a href="/wiki/Bruger:Jon_Kolbert" title="Bruger:Jon Kolbert">‪Jon Kolbert‬</a>. 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Hvis du mener, at du er blevet blokeret ved en fejl, kan du finde yderligere oplysninger og instruktioner i den globale politik <a href="https://meta.wikimedia.org/wiki/Special:MyLanguage/No_open_proxies" class="extiw" title="m:Special:MyLanguage/No open proxies">Ingen åbne proxyer</a>. </p> Du kan også diskutere blokeringen ved at <a href="https://meta.wikimedia.org/wiki/Steward_requests/Global" class="extiw" title="m:Steward requests/Global">lægge en anmodning om gennemgang på Meta-Wiki</a>. ⧼wikimedia-globalblocking-blockedtext-mistake-e-mail-steward⧽</div></div><hr /> <p>Du kan se og kopiere kildeteksten for denne side </p><textarea readonly="" accesskey="," id="wpTextbox1" cols="80" rows="25" style="" class="mw-editfont-monospace" lang="da" dir="ltr" name="wpTextbox1">{{ingen kilder|dato=september 2011}} [[Fil:Bijection.svg|thumb|200px|En bijektiv funktion.]] En [[afbildning (matematik)|afbildning]] <math>\phi:X\to Y</math> er '''bijektiv''' ('''enentydig'''), når den både er [[injektiv]] og [[surjektiv]], og man siger at <math>\phi</math> er en '''bijektion'''. En bijektiv afbildning afbilder således til ethvert element i <math>Y</math> ét (og kun ét) element i <math>X</math>; dvs. alle elementer i <math>X</math> og <math>Y</math> "er med" i afbildningen, og hverken den "forlæns" eller den "baglæns" afbildning afbilder til to elementer. Bijektioner spiller en væsentlig rolle inde for alle grene af [[matematik]]ken. Specielt er bijektionerne præcis de [[invertibel|invertible]] afbildninger. Altså findes til en bijektion <math>\phi:X\to Y</math> en entydigt bestemt afbildning <math>\phi^{-1}:Y\to X</math> sådan at <math>\phi\circ\phi^{-1} = \phi^{-1}\circ\phi</math>. Omvendt gælder, at hvis en afbildning <math>\phi</math> har en [[invers]], da er <math>\phi</math> bijektiv. Bijektioner bruges bl.a. indenfor mængdelære, hvor to mængder, X og Y, har samme [[kardinalitet]], hvis der findes en bijektion, <math>\phi:X\to Y</math>. ==Se også== * [[Isomorfi]] {{Matematikstub}}{{Filostub}} [[Kategori:Funktioner]] </textarea><div class="templatesUsed"><div class="mw-templatesUsedExplanation"><p>Skabeloner der er brugt på denne side: </p></div><ul> <li><a href="/wiki/Skabelon:Ambox" title="Skabelon:Ambox">Skabelon:Ambox</a> (<a href="/w/index.php?title=Skabelon:Ambox&action=edit" title="Skabelon:Ambox">vis kildekode</a>) (etableret bruger-beskyttet)</li><li><a href="/wiki/Skabelon:Artikel_eller_andet" title="Skabelon:Artikel eller andet">Skabelon:Artikel eller andet</a> (<a href="/w/index.php?title=Skabelon:Artikel_eller_andet&action=edit" title="Skabelon:Artikel eller andet">vis kildekode</a>) (skabelonredaktør-beskyttet)</li><li><a href="/wiki/Skabelon:Filostub" title="Skabelon:Filostub">Skabelon:Filostub</a> (<a 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