“…The elementary union (F, P ) = (G, P ) ⋓ (H, P ) and elementary intersection (F, P ) = (G, P ) ⋒ (H, P ) of (G, P ), (H, P ) ∈ S(Ũ ) are defined by (F, P ) = SS(SE(G, P ) ∪ SE(H, P )) and (F, P ) = SS(SE(G, P ) ∩ SE(H, P )), respectively. (For details, see [16,20,28,42]).…”