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离散数学学习笔记——集合运算的基本等式
集合运算的基本等式
设 U U U 为全集, A , B , C A, B, C A,B,C 为任意集合。
(1) A ∪ A = A , A ∩ A = A . A \cup A=A, A \cap A=A . \quad A∪A=A,A∩A=A. (幂等律)
(2) A ∪ B = B ∪ A , A ∩ B = B ∩ A A \cup B=B \cup A, A \cap B=B \cap A A∪B=B∪A,A∩B=B∩A. (交换律)
(3) A ∪ ( B ∪ C ) = ( A ∪ B ) ∪ C , A ∩ ( B ∩ C ) = ( A ∩ B ) ∩ C A \cup(B \cup C)=(A \cup B) \cup C, A \cap(B \cap C)=(A \cap B) \cap C A∪(B∪C)=(A∪B)∪C,A∩(B∩C)=(A∩B)∩C (结合律)
(4) A ∪ ∅ = A , A ∩ U = A A \cup \varnothing=A, A \cap U=A A∪∅=A,A∩U=A. (同一律)
(5) A ∪ U = U , A ∩ ∅ = ∅ A \cup U=U, A \cap \varnothing=\varnothing A∪U=U,A∩∅=∅. (零律)
(6) A ∪ ( B ∩ C ) = ( A ∪ B ) ∩ ( A ∪ C ) , A ∩ ( B ∪ C ) = ( A ∩ B ) ∪ ( A ∩ C ) A \cup(B \cap C)=(A \cup B) \cap(A \cup C), A \cap(B \cup C)=(A \cap B) \cup(A \cap C) A∪(B∩C)=(A∪B)∩(A∪C),A∩(B∪C)=(A∩B)∪(A∩C) (分配律)
(7) A ∪ ( A ∩ B ) = A , A ∩ ( A ∪ B ) = A A \cup(A \cap B)=A, A \cap(A \cup B)=A A∪(A∩B)=A,A∩(A∪B)=A. (吸收律)
(8) A ˉ ∩ A = ∅ , A ˉ ∪ A = U . \bar{A} \cap A=\varnothing, \bar{A} \cup A=U . \quad Aˉ∩A=∅,Aˉ∪A=U. (矛盾律和排中律)
(9) A ˉ ‾ = A . \begin{array}{ll}\text { } \overline{\bar{A}}=A . & \text { }\end{array} Aˉ=A. (双重否定律)
(10 A ∪ B ‾ = A ˉ ∩ B ˉ , A ∩ B ‾ = A ˉ ∪ B ˉ . \overline{A \cup B}=\bar{A} \cap \bar{B}, \overline{A \cap B}=\bar{A} \cup \bar{B} . A∪B=Aˉ∩Bˉ,A∩B=Aˉ∪Bˉ. (德摩根律)
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