Math : Axioms as Formulae
TOC
Listing
The Listing
Closure, Totality
Commutativity
left-commutative
right-commutative
both-sided, total commutativity
the diagram commutes
Distributivity (De Morgan's)
Identity (both-sided, left, right; additive, multiplicative; composition)
Invertability
Idempotency
Fix-point
Cyclicality
Monotonicity
Trichotomy
Reflexivity
Symmetry
Transitivity
Annihilation
Absorption
Monotonicity
Involution
Absorption
Absorption in Boolean Algebra
Absorption 1:
Absorption 2:
Annihilation
Annihilation in Boolean Algebra
Annihilator for
Annihilator for
Associativity
Associativity of a binary operation in a group
add, mul, function composition
Commutativity
Both-sided commutativity
Left commutativity
Right commutativity
(binary operations have commutativity, binary relations have symmetry)
Distributivity
a(b + c) = ab + ac
De Morgan's laws
In math logic: ¬(p ∧ q) = ¬p ∨ ¬q
Monotonicity
In Boolean Algebra, conjunction and disjunction are monotone operations because they both have the property that changing either argument, either leaves the output unchanged or the output changes in the same way as the input. In other words, changing any variable from 0 to 1 never results in the output changing from 1 to 0. Operations with this property are said to be monotone.
Nonmonotonicity enters Boolean Algebra via NOT operator, ¬.
Trichotomy
If a and b are real numbers, then one and only one of the following three statements is true: a < b, a = b, or a > b.
Totality
Closure of R+: If a and b are positive real numbers, then so are a + b and ab.
Invertability
Additive Inverse: negated number, 3 and -3
Multiplicative Inverse: reciprocal, 8 and 1/8
Addition law for inequalities
If a, b, and c are real numbers and a < b, then a + c < b + c.
The well ordering axiom
Every nonempty set of positive integers contains a smallest integer.
The least upper bound axiom
Every nonempty set of real numbers that has an upper bound has a least upper bound.
Interchange law
(x∗y)⋅(z∗w) = (x⋅z)∗(y⋅w)
in the presence of a two-sided common unit element, implies commutativity and associativity of ∗ and ⋅ (in fact, they have to be the same operation)
Substitution
If a = b, then b may be substituted for a in any mathematical statement without affecting its truth value.
Identity
Identity (neutral) element
Left identity:
Right identity:
Two-sided identity:
Additive identity: 0
Multiplicative identity: 1
Idempotence
Idempotence is the property of certain operations whereby they can be applied multiple times without changing the result beyond the initial application.
The concept of idempotence arises in a number of places in abstract algebra (in particular, in the theory of projectors and closure operators) and functional programming (in which it is connected to the property of referential transparency).
The term was introduced by Benjamin Peirce in the context of elements of algebras that remain invariant when raised to a positive integer power, and literally means "(the quality of having) the same power", from idem + potence (same + power).
In math, an idempotent operation is one where f(f(x)) = f(x)
f...(f(f(x))...) = f(x)
f is idempotent:
f: x ↦ y
f(x) = x' f(f(x)) = f(x) f(x') = x'
f(x) = y ∧ f(y) = y -> x = y ✘
f(x) = y ∧ f(f(x)) = y ->
[y/f(x)] f(x) = f(y)
f(f(x)) = f(x) = f(y) = y
f(f(x)) = f(y)
For example, the abs()
function is idempotent: ∀x . abs(abs(x)) = abs(x)
Cyclicality
Cyclicality is a property of a function that cycles between two return values.
f(x) = 1/x :: f(5) = 0.2, f(0.2) = 5, f(5) = 0.2, ...
f(x) = y ∧ f(y) = x
f(x) = f(f(x))
Fix-point
A function's fix-point is the input x for which the output gives the same value, f(x) = x.
A trivial example is x = ±1 in f(x) = x^2, meaning 1 is the fix-point of the squaring function.
Some functions have infinite number of fix-points (identity function), while others have none, e.g. f(x) = x+1
An interesting example of a function that, given given any input, works toward a fix-point is cosine function.
fix cos x = cos . cos x
Start with x=1 and after n-folds on itself, the function will fix on a constant value, i.e. a fixed-point value of 0.7390851332151607
, such that
cos(0.7390851332151607) = 0.7390851332151607
Relations
Reflexivity
reflexive
irreflexive
anti-reflexive
Symmetry
symmetric
asymmetric
anti-symmetric
Transitivity
transitive
anti-transitive
Trichotomy
Sets
axiom of comprehension
axiom of extensionality
axiom of well-definedness
Boolean logic
Identity
Absorption
Idempotency
Negation
Absorption
ML
Transformation rules
Rules of inference (Propositional calculus)
Junctions
Conjunction
introduction/elimination
Disjunction
introduction/elimination
Implication
introduction/elimination, modus ponens
Biconditional
introduction/elimination
syllogism
Disjunctive syllogism
hypothetical syllogism
dilemma
Constructive dilemma
destructive dilemma
Absorption
modus tollens, modus ponendo tollens
Rules of replacement
Associativity: (p ⩙ q) ⩙ r = p ⩙ (q ⩙ r), where ⩙ is a junction op
Commutativity
Distributivity
Double negation
De Morgan's laws
Transposition
Material implication
Exportation
Tautology
Negation
Negation introduction/elimination
Double negation introduction/elimination
Predicate logic
Universal generalization/instantiation
Existential generalization/instantiation
misc
Well-formedness
the law of bivalence (either true or false, not both nor neither)
the law of excluded middle
Identity,
ID
soundness, us-
completeness, in-
compactness
Validity
Cogency
consistency
Independence
Axioms of Algebra
An Axiom is a mathematical statement that is assumed to be true. There are four rearrangement axioms and two rearrangement properties of algebra. Addition has the commutative axiom, associative axiom, and rearrangement property. Multiplication has the commutative axiom, associative axiom, and rearrangement property.
Commutative Axiom for Addition
The order of addends in an addition expression does not matter.
For example: x + y = y + x
Commutative Axiom for Multiplication
The order of factors in a multiplication expression does not matter.
-For example: xy = yx
Associative Axiom for Addition
In an addition expression it does not matter how the addends are grouped.
For example: (x + y) + z = x + (y + z)
Associative Axiom for Multiplication
In a multiplication expression it does not matter how the factors are grouped. For example: (xy)z = x(yz)
Rearrangement Property of Addition
The addends in an addition expression may be arranged and grouped in any order.
This is a combination of the associative and commutative axioms.
e.g. x + y + z = x + (y + z) = (x + y) + z = z + (y + x) = y + (z + x)
Rearrangement Property of Multiplication
The factors in a multiplication expression may be arranged and grouped in any order.
This is a combination of the associative and commutative axioms.
e.g. xyz = x(yz) = z(yx) = y(zx)
Zero Product
Branches
Logic: propositions
Number theory
Algebra
Sets
Relations
CS
recursive, recursion
decidability
computability
In computability theory, a set of natural numbers is called recursive, computable or decidable if there is an algorithm which takes a number as input, terminates after a finite amount of time (possibly depending on the given number) and correctly decides whether the number belongs to the set or not.
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