De Morgan's law states that (A∪B)c(A \cup B)^c(A∪B)c is equal to:
Ac∪BcA^c \cup B^cAc∪Bc
Ac∩BcA^c \cap B^cAc∩Bc
A∩BA \cap BA∩B
Ac∖BcA^c \setminus B^cAc∖Bc