Ib txheej hu ua suav tau yog tias nws yog qhov kawg lossis suav tsis kawg. Yeej, ib qho teeb meem tsis kawg yog suav tau yog tias nws cov ntsiab lus tuaj yeem teev nyob rau hauv ib qho kev sib koom ua ke thiab koom nrog. "Listable" tej zaum yuav yog lo lus zoo dua, tab sis nws tsis yog siv tiag tiag. Yog li cov teeb N thiab Z muaj tib lub cardinality.
Puas tag nrho cov teeb muaj cardinality?
Kev sib piv
N tsis muaj tib daim cardinality raws li nws lub hwj chim teeb P(N): Rau txhua txoj haujlwm f los ntawm N rau P(N), qhov teeb tsa T={n∈N: n∉f(n)} tsis pom zoo nrog txhua qhov teeb tsa hauv thaj tsam ntawm f, li no f tsis tuaj yeem ua tiav.
Dab tsi yog qhov khoom plig?
Lub cardinality ntawm ib lub teeb yog ib qho ntsuas ntawm ib lub teeb qhov loj, lub ntsiab lus ntawm cov ntsiab lus hauv lub teeb. Piv txwv li, lub teeb A={ 1, 2, 4 } A=\{1, 2, 4} A={1, 2, 4} muaj ib tug cardinality ntawm 3 rau peb lub ntsiab lus uas muaj nyob rau hauv nws.
Puas tag nrho cov finite sets muaj tib cardinality?
Txhua yam sib npaug rau qhov tsis muaj nuj nqis kawg A yog qhov kawg thiab muaj tib daim cardinality li A. Piv txwv tias A yog ib qho kev txwv tsis pub dhau, B yog txheej, thiab A≈B. Txij li thaum A yog ib qho kev txwv tsis pub dhau, muaj ib qho k∈N xws li A≈Nk.
Puas cov teev N thiab Z muaj tib daim cardinality?
1, the sets N thiab Z muaj tib yam cardinality. Tej zaum qhov no tsis yog qhov xav tsis thoob, vim tias N thiab Z muaj qhov muaj zog geometric zoo ib yam li cov ntsiab lus ntawm kab zauv. Dab tsi yog qhov xav tsis thoob yog tias N (thiab yog li Z)muaj tib lub cardinality raws li lub teeb Q ntawm txhua tus lej rational.
