olemus
funktsioon c, mis mingi hulga S igale alamhulgale X seab vastavusse hulga S alamhulga c(X ), nii et kehtivad
(i) laienduvus: X on hulga c(X ) alamhulk
(ii) monotoonsus: kui hulk X on hulga Y alamhulk,
siis hulk c(X) on hulga c(Y) almhulk
(iii) idempotentsus: c(c(X )) = c(X )
Wiktionary:
a closure operator on the poset P is a function C : P → P that is monotone, idempotent, and satisfies C(x) ≥ x for all x in P

näide: hulga X kumer kate c(X )

ülevaateid
https://en.wikipedia.org/wiki/Closure_operator
https://ncatlab.org/nlab/show/closure+operator
https://www.ams.org/journals/tran/1944-055-00/S0002-9947-1944-0010556-9/S0002-9947-1944-0010556-9.pdf

vt ka
- sulund
- sulundiruum