山东大学离散数学1知识点整理
离散数学
第一章:基础:逻辑与证明
1.1命题逻辑:Propositons Logic
1、命题Propositons:
- A proposition is a declarative(陈述的) sentence that is either true or false.
否定:Negation
- The negation of a proposition p is denoted by ¬p.
合取:Conjunction
- The conjunction of propositions p and q is denoted by p ∧ q
析取:Disjunction
- The disjunction of propositions p and q is denoted by p ∨q.
蕴含:Implication
- If p and q are propositions, then p →q is a conditional statement or implication which is read as “if p, then q ”
等价:Biconditional
- If p and q are propositions, then we can form the biconditional proposition p ↔q , read as “p if and only if q .” The biconditional p ↔q denotes the proposition with this truth table.
1.3命题等价式
永真式:tautology
- A tautology is a proposition which is always true.
- Example: p ∨¬p
矛盾式:contradiction
- A contradiction is a proposition which is always false.
- Example: p ∧¬p
可能式:contingency
- A contingency is a proposition which is neither a tautology nor a contradiction
逻辑等价式:Logically Equivalent
逻辑等价式
条件命题逻辑等价式
双条件命题逻辑等价式
1.4谓词逻辑:Predicate Logic
命题函数Proposional Funcons
量词
全称量词:Universal Quantifier
存在量词:Existen Quantifier
量词优先级:Precedence of Quantifier
- The quantifiers ∀ and ∃ have higher precedence than all the logical operators.
- For example, ∀x P(x)∨Q(x) means (∀x P(x))∨Q(x).
- ∀x(P(x)∨Q(x)) means something different
设计量词的逻辑等价式:Equivalences in Predicate Logic
1.5嵌套量词Nested Quantifiers
- Nested quantifiers are often necessary to express the meaning of sentences in English as well as important concepts in computer science and mathematics.
- Example: “Every real number has an additive inverse” ∀x∃y(x + y = 0)
- where the domains of x and y are the real numbers.
- We can also think of nested propositional functions: ∀x∃y(x + y = 0) can be viewed as ∀xQ(x) where Q(x) is ∃yP(x, y) where P(x, y) is (x + y = 0)
量词的顺序:Order of Quantifiers
- ∀x∀y P(x, y)
- 何时为真:对每一对x、y,P(x,y)都为真。
- 何时为假:存在一对x、y,使得P(x,y)为假。
- ∀x∃y P(x, y)
- 何时为真:对每个x,都存在一个y使得P(x,y)为真。
- 何时为假:存在一个x,使得P(x,y)总为假。
- ∃x∀y P(x, y)
- 何时为真:存在一个x,使得P(x,y)对所有的y均为真。
- 何时为假:对每个x,存在一个y,使得P(x,y)为假。
- ∃x∃y P(x, y)
- 何时为真:存在一对x、y,使P(x,y)为真。
- 何时为假:对每一对x、y,P(x,y)均为假。
1.6推理规则
有效论证:Valid Arguments
- 定义1:An argument in propositional logic is a sequence of propositions. All but the final proposition are called premises. The last statement is the conclusion.
- 命题逻辑中的一个论证是一连串的命题。除了论证中最后一个命题外都叫做前提,最后那个命题叫做结论。
- The argument is valid if the premises imply the conclusion.
- 如果这个命题的前提可以蕴含结论,那么这个论证是有效的。
- 命题逻辑中的论证形式是一连串涉及命题变量的复合命题。无论用什么特定命题来替换其中的命题变量,如果前提均真时结论为真,则称该论证形式是有效的。
常见的推理规则
量化命题的推理规则
第二章:基本结构:集合、函数
- Basic Structures:Set,Functions
2.1集合 Sets
集合 Sets
- A set is an unordered collection of objects.The objects in a set are called the elements, or members of the set. A set is said to contain its elements.The notation a ∈ A denotes that a is an element of the set A.
- 确定性:一个元素是否属于这个集合是确定的。
- 无序性:集合中的元素没有顺序
- 元素互异性:集合中的元素互不相同
集合相等:Set Equality
- Two sets are equal if and only if they have the same elements. Therefore if A and B are sets, then A and B are equal if and only if (对于任意x(x属于A<—>x属于B)) We write A = B if A and B are equal sets.
- 两个集合相等当且仅当他们拥有相同的元素。所以,如果A和B是集合,则A和B是相等的当且仅当对于任意x(x属于A<—>x属于B)。如果A和B是相等的集合,那么记作A = B。
子集:Subset
- The set A is a subset of B, if and only if every element of A is also an element of B.The notation A ⊆ B is used to indicate that A is a subset of the set B. A ⊆ B holds if and only if is对于任意x(x属于A—>x属于B) true.
Another look at Equality of Sets
真子集:Proper Subsets
- If A ⊆ B, but A ≠B, then we say A is a proper subset of B, denoted by A ⊂ B. If A ⊂ B,
集合的基数:Set Cardinality
- If there are exactly n distinct elements in S where n is a nonnegative integer, we say that S is finite. Otherwise it is infinite.The cardinality of a finite set A, denoted by |A|, is the number of (distinct) elements of A.
- finite 有限的 distinct 不同的
- 一个集合称为无限的,如果它是有限的。
幂集:Power Sets
- The set of all subsets of a set A, denoted P(A), is called the power set of A.
- 所有子集的集合:这是一个集合的集合
元组:Tuples
- The ordered n-tuple (a1,a2,…..,an) is the ordered collection that has a1 as its first element and a2 as its second element and so on until an as its last element.
- 有序
- Two n-tuples are equal if and only if their corresponding elements are equal.
- The ordered pairs (a,b) and (c,d) are equal if and only if a = c and b = d
- 有序二元组是相等的当且仅当每一对对应的元素都相等。
- 2-tuples are called ordered pairs.有序对
笛卡尔积:Cartesian Product
2.2集合运算 Set Operation
并集:Union
- Let A and B be sets. The union of the sets A and B, denoted by A ∪ B.
- 令A和B为集合。集合A和B的并集,用A ∪ B表示,是一个集合,他包含A或者B中或同时在A和B中的元素。
交集:Intersection
- The intersection of sets A and B, denoted by A ∩ B.
- 令A和B为集合,集合A和B的交集,用A ∩ B表示,是一个集合,他包含同时存在A和B中的那些元素。
补集:complement
- If A is a set, then the complement of the A (with respect to U), denoted by Ā
- 令U为全集。集合A的补集,用Ā表示,是A相对于U的补集。所以集合A的补集是U - A。
差集:Difference
- Let A and B be sets. The difference of A and B, denoted by A – B, is the set containing the elements of A that are not in B. The difference of A and B is also called the complement of B with respect to A.
- 令A和B为集合。A和B的差集,用A - B表示,是一个集合,他包含属于A而不属于B的元素。A和B的差集也称为B相对于A的补集。
集合恒等式:
德摩根律啥的
证明集合恒等式的方法
- 子集方法:证明恒等式的每一边是另一边的子集
- 成员表:对于原子集合的每一种可能的组合,证明恰好在这些原子集合中的元素要么同时属于两边,要么都不属于两边。
- 应用已知的恒等式:从一边开始,通过应用一系列已经建立了的恒等式将它转换成另一边的形式。
函数:Function
- 函数有时候也称为映射(mapping)或者变换(transformation)。
- Let A and B be nonempty sets. A function f from A to B, denoted f: A → B is an assignment of each element of A to exactly one element of B. We write f(a) = b if b is the unique element of B assigned by the function f to the element a of A.
- 令A和B为非空集合。从A到B的函数f是对元素的一种指派,对A的每个元素恰还指派B的一个元素。如果B中元素b是唯一由函数f指派给A中元素a的,则我们就写成f(a) = b。如果f是从A到B的函数,就写成f:A - > b。
- 如果f是从A到B的函数,我们说A是f的定义域(domain),而B是f的陪(codomain)。如果f(a) = b,我们说b是a的像(image),而a是b的原像(preimage)。f的值域(range)或像是A中元素的所有像的集合。如果f是从A到B的函数,我们说f把A映射(map)到B上。
一对一函数:one-to-one
- A function f is said to be one-to-one , or injective, if and only if f(a) = f(b) implies that a = b for all a and b in the domain of f. A function is said to be an injection if it is one-to-one.
- 对任意a和任意b,如果f(a) = f(b) 那么 a = b。
- 又叫单射(injection)函数
映上函数:onto
- A function f from A to B is called onto or surjective, if and only if for every element there is an element a 属于A with f(a) = b. A function f is called a surjection if it is onto.
- 任意y 都存在x 使 f(x) = y。
- 又叫满射(surjection)函数
双射函数:bijection
- A function f is a one-to-one correspondence, or a bijection, if it is both one-to-one and onto (surjective and injective).
- 既是单射又是满射。
- 又叫一一对应(one-to-one correspondence)函数。
反函数:inverse functions
复合函数:composition
关系:Relations
9.1、关系及其性质:relations and their property
二元关系:binary relation
- A binary relation R from a set A to a set B is a subset R ⊆ A × B.
- 设A和B是集合,,一个从A到B的二元关系是A与B的笛卡尔积的子集。
在一个集合上的二元关系:binary relation on a set
- A binary relation R on a set A is a subset of A × A or a relation from A to A.
定义二:一个集合A上的关系是从A到A的关系。
自反关系:Reflexive Relation
- R is reflexive iff (a,a) ∊ R for every element a ∊ A. Written symbolically.
- 若对每个属于A的元素a,都有(a,a)属于R,那么定义在集合A上的关系R称为自反的。
对称关系:symmetric relations
- R is symmetric iff (b,a) ∊ R whenever (a,b) ∊ R for all a,b ∊ A. Written symbolically。
反对称关系:Antisymmetric Relations
- A relation R on a set A such that for all a,b ∊ A if (a,b) ∊ R and (b,a) ∊ R, then a = b is called antisymmetric. Written symbolically
- 可视化表达里,反对称关系要求两个元素之间只能有一个箭头。
- 对称关系和反对称关系不是对立的,一个集合可以同时满足对称和反对称,也可以同时不满足。
传递关系:Transitive Relations
- A relation R on a set A is called transitive if whenever (a,b) ∊ R and (b,c) ∊ R, then (a,c) ∊ R, for all a,b,c ∊ A. Written symbolically,
Combining Relations
- Given two relations R1 and R2 , we can combine them using basic set operations to form new relations such as R1 ∪ R2 , R1 ∩ R2 , R1 − R2 , and R2 − R1
合成:composition
- Suppose
- R1 is a relation from a set A to a set B.
- R2 is a relation from B to a set C.
- Then the composition (or composite) of R2 with R1, is a relation from A to C where
- if (x,y) is a member of R1 and (y,z) is a member of R2, then (x,z) is a member of R2∘R1.
一个关系自身的合成:Compositon of a relation with itself
- Suppose R is a relation on a set A. Then the composition (or composite) of R with R, denoted by R∘ R, is a relation on A where if (x,y) is a member of R and (y,z) is a member of R, then (x,z) is a member of R∘ R.
关系的幂:powers of a relation
- 递归的 recursive
定理一:
- The relation R on a set A is transitive iff Rn ⊆ R for all positive integers n.
9.4闭包:closure
- 闭包:设R是集合A上的关系,若存在关系R的具有性质P的闭包,则此闭包是集合A上包含的具有性质P的关系S,并且S是每一个包含R的具有性质P的A×A的子集。
9.5等价关系:Equivalence Relations
- A relation on a set A is called an equivalence relation if it is reflexive, symmetric, and transitive.
- 一个定义在A上的关系叫做等价关系,如果它是自反的,对称的,传递的。
- Two elements a, and b that are related by an equivalence relation are called equivalent. The notation a ∼ b is often used to denote that a and b are equivalent elements with respect to a particular equivalence relation.
等价类:Equivalence Classes
- Let R be an equivalence relation on a set A. The set of all elements that are related to an element a of A is called the equivalence class of a. The equivalence class of a with respect to R is denoted by [a]R. When only one relation is under consideration, we can write [a], without the subscript R, for this equivalence class.
等价类与划分:Equivalence Classes and Partitions
- Let R be an equivalence relation on a set A. These statements for elements a and b of A are equivalent:
- (i) aRb
- (ii) [a] = [b]
- (iii) [a] ∩ [b] ≠ ∅
5.6偏序:Partial Orderings
偏序:Partial Orderings
- A relation R on a set S is called a partial ordering, or partial order, if it is reflexive, antisymmetric, and transitive.
- 定义在集合S上的关系R,如果它是自反的,反对称的和传递的,就称为偏序
- A set together with a partial ordering R is called a partially ordered set, or poset, and is denoted by (S, R). Members of S are called elements of the poset.
- 集合S与定义在其上的偏序R一起称为偏序集,记作(S,R)。集合S中的成员称为偏序集的元素。
可比性:Comparability
- The elements a and b of a poset (S,≼ ) are comparable if either a ≼ b or b ≼ a. When a and b are elements of S so that neither a ≼ b nor b ≼ a, then a and b are called incomparable.
- 偏序集(S, ≼)中的元素a和b称为可比的,如果a ≼ b或b ≼ a。当a和b是S中的元素并且既没有a ≼ b也没有b ≼ a,则称a和b是不可比的。
- If (S,≼) is a partially ordered set and every two elements of S are comparable, S is called a totally ordered or linearly ordered set, and ≼ is called a total order or a linear order. A totally ordered set is also called a chain.
- 如果(S,≼)是偏序集,且S中的每对元素都是可比的,则S称为全序集或线序集,且≼称为全序或线序,一个全序集也称为链。
哈塞图:Hasse Diagrams
三条原则:
- 去自环。
- 只保留盖住关系。
- 箭头方向都是往上指,去掉箭头。
- A Hasse diagram is a visual representation of a partial ordering that leaves out edges that must be present because of the reflexive and transitive properties.
- Hasse图是部分排序的可视化表示,它去掉了由于自反性和传递性而必须存在的边。
盖住关系:
- 设(S, ≼)是一个偏序集。若x < y且不存在z属于S使得 x < z < y,则称元素y属于S覆盖元素x属于S。y覆盖x有序对(x,y)的集合称为(S, <=)的覆盖关系。
极大元与极小元:Maximal and Minimal Elements
极大元极小元:Maximal and Minimal Elements
- 偏序集中的一个元素称为极大元,当它不小于这个偏序集的任何其他元素。
- 既不存在b属于S使得a < b,a在偏序集(S,<=)中是极大元。
- 类似的 偏序集中的一个元素称为极小元,当它不大于这个偏序集的任何其他元素。
- 既不存在b属于S使得a > b,a在偏序集(S,<=)中是极小元。
- 极大元极小元都不一定唯一,也不一定存在。
- 无穷偏序集就可以都没有,但是也可以有。
- 有限偏序集一定存在极大元和极小元
最大元与最小元:Greatest element and least element
- 有时在偏序集中存在一个元素大于每一个其他的元素。这样的元素称为最大元。
- 即a是偏序集(S , <=)的最大元,如果对所有的b属于S都有b <= a。
- 当极大元存在的时候,他是唯一的。
- 类似的 有时在偏序集中存在一个元素小于每一个其他的元素。这样的元素称为最小元。
- 即a是偏序集(S , <=)的最小元,如果对所有的b属于S都有b >= a。
- 当极小元存在的时候,他是唯一的。
上界与下界:Upper bound and lower bound
- 有时候可以找到一个元素大于或等于偏序集(S , <=)的子集A中的任何一个元素。如果u是S中的元素,使得对所有的a属于A,有a <= u,那么u称为A的一个上界。
- 类似的 有时候可以找到一个元素小于或等于偏序集(S , <=)的子集A中的任何一个元素。如果u是S中的元素,使得对所有的a属于A,有a >= u,那么u称为A的一个下界。
- 上届下界也可能是这个集合中的元素。
- 上届下界可能存在多个,也可能不存在。
上确界与下确界:least upper bound and greatest lower bound
- 上确界:上界中最小的那一个。
- 下确界:下界中最大的那一个。
- 有可能不存在:不存在的原因可以是因为:存在必唯一,也是由于其他的原因。
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