Memorise! Flashcards
Truth table Implication
A | B | Output
0 0 1
0 1 1
1 0 0
1 1 1
Truth table bi-implication
A | B | Output
0 0 1
0 1 0
1 0 0
1 1 1
Simplification of Implication
a => b = not(a)Vb
Simplification of Bi-Implication
a <=> b = (a=>b) n (b=>a)
Tautology
Proposition that is always true
Contradiction
Proposition that is always false
Contingency
Proposition that is not a tautology or contradiction
Definition of Consequence
Q is a logical consequence of D if for every “output value”, if D evaluates to True, then Q evaluates to True
D|= Q
Definition of Comparable
If Q is a logical consequence of P, or P is a logical consequence of Q, then they are comparable
Definition of Strongness & Weakness
False is strongest, True is weakest
P is a logical consequence of Q = P is stronger then Q, Q is weaker then P
De Morgan’s law for Quantifiers
not Ax[P:Q] = Ex[P: not q]
not Ex[P:Q] = Ax[P:not q]
Introduction and Elimination Rules for Conjunction, Disjunction, Implication, Bi-implication, Negation, Contradiction, Double Negation, Contraposition, Case Distinction
write it!
Introduction and Elimination Rules for Universal and Existentisal Quantification
5 in total!
(universal intro &elim)
(existensial intro &elim)
(normal existensial intro)
Property and Definition Rules
Property = Intro, Definition = Elim
Property and Definition Rules for =, n, u, complement, difference, empty set, subset, Powerset,
write it!
Ordered Pair
Two elements with fixed ordering (a,b), a is the first and b is the second
Property of Ordered Pair
(a,b) = (a’,b’)
logically equivalent to
(a=a’) n (b=b’)
Cartesian Product
The set of all ordered pairs (a,b) with a exists in A and b exists in B
Property of Cartesian Product
(a,b) exists in AxB
logically equivalent to
a exists in A n b exists in B
Definition of a Relation
A set of ordered pairs
Cartesian Graph
A graph that corresponds to an ordered pair that shows which are related
Arrow Graph
Draw it!
Reflexive Property Definition
Ax[x in A: xRx]
Symmetry Property Definition
Ax,y[x,y in A: xRy => yRx]
Transitivity Property Definition
Ax,y,z[x,y,z in A: xRy n yRz => xRz]
Equivalence Relation
A relation that is reflexive, symmetric and transitive
Equivalence Class
Partition of the set into classes that are related
Mapping
A relation from Set A to Set B that relates every element x in A to a element y in B
Property of Mapping
Ax[x in A: Ey^1[y in B: F(x) = y]]
Composite Mapping
research cases of injection,surjection and bijection in this context
Image
A subset of set A, A’, that is mapped to set B
Property of Image
- F(x) in F(A’) is a logical consequence of x in A’
- y in F(A’) is logically equivalent to Ex[x in A’:F(x) = y]
Source
A subset of Set B, B’, that is related to a subset of A, A’
A’ is the source of B’ with respect to F
Property of Source
x in F<-(B’) = F(x) in B’
Surjection
For every element in the codomain, there is AT LEAST one element in the domain that maps to it
Injection
For every element in the codomain, there is AT MOST one element in the domain that maps to it
Property of Surjection
Ay[y in B: Ex[x in A: F(x) = y]]
Property of Injection
Ax1,x2[x1,x2 in A: F(x1) = F(x2) => x1=x2]
Bijection
For every element in the codomain, there is EXACTLY one element in the domain that maps to it
Property of Bijection
Ay[y in B: Ex^1[x in a, F(x) = y]]
Inverse
The opposite of a mapping
from F: A->B
its F^-1: B -> A
such that for all x in A and y in B,
F^-1(y) = x, if F(x) = y
Property of Inverse
F^-1(y) = x is logically equivalent to F(x) = y
Property of Induction
write it
Property of strong induction
write it
Proving Reflexivity, Symmetry and Transitivity
Ordering
A relation on a set that organises elements of a set according to rules
Reflexive Partial Ordering
- Reflexive
- Anti-Symmetric
- Transitive
Irreflexive Partial Ordering
- Irreflexive
- Strictly Anti-Symmetric
- Transitive
Irreflexive Property
Ax[x in A: not(xRx)]
Quasi-Ordering
A structure <A,R> such that R is reflexive and transitive
Structure
A set with an ordering, such as <A,R>
A = set
R = ordering
Anti Symmetry Property
Ax,y[x,y in A: (xRy n yRx) => x=y]
Strictly Anti Symmetric Property
Ax,y[x,y in A: not(xRy n yRx)]
Hasse Diagram
Shows successors/predecessors and max/min of a structure
Maximum
There is an element for which everything is below it
Reflexive
Ax[x in A’: mRx => m=x]
Irreflexive:
Ax[x in A’: not(mRx)]
Minimum
There is an element for which everything is above it
Reflexive
Ax[x in A’: xRm => x=m]
Irreflexive
Ax[x in A’: not (xRm)]
Maximal Element
There is nothing above it
Reflexive
Ax[x in A’: xRm]
Irreflexive
Ax[x in A’ n x != m : xRm]
Minimal Element
There is nothing below it
Direct Successors
Y is a direct successor of X IF:
Reflexive:
xRy n zRy n notEz(z in A n z!=x n z!=y: xRz n zRy]
Irreflexive:
xRy n notEz[z in A: xRz n zRy]
Lexicographic Orderings
Given two ordered sets, <A,S1> and <B,S2>, the lexicographic ordering is determined by:
(a1,b1) S3 (a2,b2) if a1 S1 a2 V (a1=a2 n b1 S2 b2)
can be reflexive or irreflexive
ALL lexicographic orderings are transitive
Linear (Total) Orderings
- Reflexive
- Anti-Symmetric
- Transitive
- Comparability (for every pair of elements a,b in a set, either aRb or bRa)