On the lattice of proximities of Čech compatible with a given closure space
W. J. Thron, Richard H. Warren · Pacific Journal of Mathematics · 1973
DEFINITION 1.1.[2, p. 237] Let Xbe a set.A function c: &>(X)-+ &*(X) is called a Cech closure operator on X iff it satisfies the following three axioms: Cl: Φ = φ; 519 520 W. J. THRON AND R. H. WARREN C2: for every A c X, A c A; C3: for all i,ΰcl, A{jB = A\jB