Ib txheej suav suav tsis txheeb yog tias nws cov ntsiab lus tuaj yeem muab tso rau hauv ib-rau-ib tsab ntawv nrog cov txheej txheem ntawm tus lejHauv lwm lo lus, ib tus tuaj yeem suav tag nrho cov ntsiab lus hauv lub teeb nyob rau hauv xws li ib txoj kev uas, txawm tias qhov suav yuav siv mus ib txhis, koj yuav tau txais mus rau ib qho tshwj xeeb lub caij nyob rau hauv ib tug finite lub sij hawm.
Yuav ua li cas koj thiaj paub yog tias qhov teeb meem tsis kawg?
Cov ntsiab lus los txheeb xyuas seb lub teeb puas yog qhov kawg lossis tsis kawg yog:
- Ib qho teeb meem tsis kawg yog qhov txwv tsis pub dhau los ntawm qhov pib lossis xaus, tab sis ob sab tuaj yeem ua tau ntev. …
- Yog tias ib lub teeb muaj qhov txwv tsis pub dhau, nws yog qhov tsis kawg thiab yog tias cov ntsiab lus ntawm cov teeb suav suav tau ces nws yog qhov kawg.
Koj ua pov thawj li cas cardinality ntawm infinite teev?
A set A yog suav tsis txheeb yog thiab tsuas yog teem A muaj tib lub cardinality li N (tus lej ntuj). Yog tias teeb A yog suav tsis txheeb, ces |A|=|N|. Tsis tas li ntawd, peb xaiv lub cardinality ntawm countably infinite teev li ℵ0 ("aleph null"). |A|=|N|=ℵ0.
Puas suav suav suav tsis txheeb?
Ib txheej yog hais tias suav tau yog tias nws yog qhov kawg lossis suav tsis kawg. Txij li daim ntawv qhia tus kheej id (x)=x yogib qho kev sib tw ntawm ib qho teeb meem, txhua qhov teeb meem yog equinumerous nrog nws tus kheej, thiab yog li N nws tus kheej yog suav tsis txheeb. Lo lus "countably infinite" yog txhais tau tias yog evocative.
Yuav ua li cas tsis muaj qhov kawg yuav yog Surjective?
Yog B yog infinite, a bijection R B, uas yog li surjective. f yog qhov kev txiav txim.
