Sets And N Tuple

Sets-and-N-tuple

Sets

  • A set is a collection of objects
  • Sets are used to group objects together

Notation of Sets

  • {}
  • Expressions:
    • List all the members
      • $C={a,b,c}$
    • Use predicates
      • $E={x x\%2=0}$
    • Use suspension points
      • $S={…,-3,-2,-1}$
  • Properties:
    • No order
    • No duplicated elements

Universial Sets

  • A universal set^[通用集,泛集] is a set that contains all the objects under consideration
  • Some Common universial sets
    • ℕ : the set of all natural numbers
    • ℤ : the set of integers
    • $ℤ^+$: the set of all the positive integers
    • ℚ: the set of all rational numbers
    • ℝ: the set of all the real numbers
    • ℂ: the set of all complex numbers

Venn Diagrams

  • A Venn diagram includes two basic shapes
    • A rectangle: indicates the universal set (all the objects under consideration)
    • Circles or other shapes: indicate normal sets.

Elements and sets

  • $x \in S$: x is in or is an element of S.
  • $x \notin S$: x is not in or is not an element of S.

Subsets

  • Subsets
    • The set $S_1$ is a subsets of the set $S_2$ (denoted $S_1\subseteq S_2$) iff $\forall x(x\in S_1 \rightarrow x \in S_2)$
    • $A \subseteq A$
  • $S_1=S_2$ iff
    • $(\forall x(x \in S_1 \rightarrow x\in S_2)) \wedge (\forall x(x \in S_2 \rightarrow x\in S_1))$
    • $\forall x(x \in S_1 \leftrightarrow x\in S_2)$
    • $(S_1 \subseteq S_2) \wedge (S_2 \subseteq S_1)$
  • Proper Subsets
    • The set $S_1$ is a proper subsets of the set $S_2$ (denoted $S_1\subset S_2$) iff $\forall x(x\in S_1 \rightarrow x \in S_2) \wedge (S_1 \not= S_2)$
  • Empty sets denoted $\emptyset$

Cardinality

  • Cardinality is the number of distinct elements in a set.
    • The cardinality of a set $S$ is denoted as $ S $.
    • The Cardinality an be finite or infinite.
      • eg. $S={a,b,c,d,e}$, $ S =5$

Power Sets

  • The power sets of $S$ is $P(S)$ which is the set of all the subsets of $S$.
    • $P(S)={A A\subseteq S}$
  • The Cardinality of $ P(S) $ = $2^{ S }$^[use induction to proof]

Ordered n-tuple

  • The form $(a_1,a_2,…,a_n)$ or $<a_1,a_2,…,a_n>$
    • Called ordered n-tuple
    • The elements in the tuple are ordered
    • E.g.,
      • $(2,3)$ is a 2-tuple $(3,2)$ is a 2-tuple they are different

Cartesian Product

  • Cartesian product of two sets $S_1$ and $S_2$ denoted($S_1 × S_2$)
    • $S_1 × S_2 = {(a,b) a\in S_1 \wedge b \in S_2}$
  • if $ S_1 =m$ and $ S_2 =n$, then $ S_1 × S_2 = m × n$
  • $S_1 × S_2 \not= S_2 × S_1$
  • $S_1 × S_2 × S_3 \not= (S_1 × S_2) × S_3$

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