Answer to Question #239291 in Differential Geometry | Topology for Fozia Sayda

Question

Theorem:

(i) For any collection {G_i} of open sets YG_i is open .

(ii) For any collection {F_i} of closed set nF_i is closed .

(iii) For any finite collection G₁ , G₂ ......G_n of open sets nⁿ_iG_i is open .

(iv) For any finite collection F₁,F₂...F_n of closed sets u^x_iF_i is closed.