浙江大学：《离散数学》课程教学资源（PPT课件讲稿）第一章 命题逻辑（1.4-1.5）集合

sot 集合 1.4集合 Sets 2/24/202111:15PM Deren Chen Zhejiang univ

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 1 1.4 集合 Sets

sot 集合 集合/Sets: As a collection of some objects 2/24/202111:15PM Deren Chen Zhejiang univ 2

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 2 集合/ Sets: As a collection of some objects

DEFINITION 1 80t8 集合 The objects in a set are also called the elements or members of the set, a set is said to contain its elements Null Set: There are no anything in the set O={x|x∈P(x)∧~(x∈P(x)) 2/24/202111:15PM Deren Chen Zhejiang univ 3

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 3 DEFINITION 1. The objects in a set are also called the elements, or members, of the set. A set is said to contain its elements. Null Set: There are no anything in the set. Ø={x | xP(x) ∧ (x P(x) )}

EXAMPLE1 80t8 集合 The set v of all vowels in the english alphabet can written as --- V=a, e, i, 0, u. 2/24/202111:15PM Deren Chen Zhejiang univ

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 4 EXAMPLE 1 The set V of all vowels in the English alphabet can written as ---- V = {a, e, i, o, u}

EXAMPLE 2 80t8 集合 The set o of odd positive integers less than 10 can be xpressed by O={1,3,5,7,9} O={x|x>=1∧x<=10∧ x is odd number} A={a,b,c,…,n}枚举法 A={x|x∈P(x)}谓词公式法/ set builder 2/24/202111:15PM Deren Chen Zhejiang univ

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 5 EXAMPLE 2 The set O of odd positive integers less than 10 can be expressed by O = {1, 3, 5, 7, 9}. O = {x | x >=1 ∧ x <=10 ∧x is odd number}. A = {a, b, c, …… n} 枚举法 A = {x | xP(x)} 谓词公式法/set builder

DEFINTION 2. 80t8 集合 Two sets are equal if and only if they have the same elements. Presented as A=B otherwise a= B A=B分Vx(x∈A+x∈B) 2/24/202111:15PM Deren Chen Zhejiang univ

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 6 DEFINTION 2. Two sets are equal if and only if they have the same elements. Presented as A=B otherwise A  B A = B   x ( x  A  x  B)

EXAMPLE 5 80t8 集合 The sets ( 1, 3, 5 and 3, 5, 1 are equal, since they have the same elements note that the order in which the elements of a set are listed does not matter. note also that it does not matter if an element of a set is listed more than once, so that (1, 3, 3,, 5 is the same as the set (1, 3, 5 since they have the same elements. 2/24/202111:15PM Deren Chen Zhejiang univ

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 7 EXAMPLE 5 The sets {1, 3, 5} and {3, 5, 1} are equal, since they have the same elements. Note that the order in which the elements of a set are listed does not matter. Note also that it does not matter if an element of a set is listed more than once, so that {1, 3, 3, 3, 5, 5, 5, 5} is the same as the set {1, 3, 5} since they have the same elements

sot 集合 l、集合中的元素互异 2、集合中的元素无次序和大小之分 3、集合中的元素不一定同类 集合中的元素也可以是集合 2/24/202111:15PM Deren Chen Zhejiang univ

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 8 1、集合中的元素互异 2、集合中的元素无次序和大小之分 3、集合中的元素不一定同类 4、集合中的元素也可以是集合

DEFINITION 3 80t8 集合 The set a is said to be a subset of B if and only if every element of a is also an element of B. we use the notation acb to indicate that a is a subset of the set B A是B的子集、 B包含A、 A包含在B中 2/24/202111:15PM Deren Chen Zhejiang univ

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 9 DEFINITION 3. The set A is said to be a subset of B if and only if every element of A is also an element of B. We use the notation AB to indicate that A is a subset of the set B. A是B的子集、 B包含A、 A包含在B中

sot 集合 The set a is said to be a proper subset of B ifAcB and there is a∈ B and agA A是B的真子集、 B真包含A、 A真包含在B中 2/24/202111:15PM Deren Chen Zhejiang univ

S e t s 集合 2/24/2021 11:15 PM Deren Chen, Zhejiang Univ. 10 The set A is said to be a proper subset of B if AB and there is aB and aA A是B的真子集、 B真包含A、 A真包含在B中