اذا كانت A equals open curly brackets space 1 space comma space space 2 space comma space 3 space space close curly brackets space space space comma space space B equals open curly brackets space 3 space comma space 4 space close curly brackets فان A minus B equals
right to left empty set
open curly brackets space 1 space comma space space 2 space comma space 3 space space close curly brackets space
open curly brackets space 3 space comma space 4 space close curly brackets
open curly brackets space 1 space comma space space 2 space space close curly brackets