Vocab. Flashcards
axiomatic system parts
1) Undefined terms
2) Definitions
3) Axioms
4) Theorems
5) Proofs
undefined terms (In an Axiomatic System)
A minimal number of technical words that will be used in the subject that we will not explicitly define.
definitions (In an Axiomatic System)
Used to allow statements to be made concisely and to identify and highlight key structures and concepts.
axioms (In an Axiomatic System)
Used interchangeably with postulate, they are statements that are accepted without proof. They are where the subject begins and everything else in the system should be logically deduced from them.
theorem/proof
Can be used synonymously, they are statements that are proved using the axioms. The 1st proof uses only the axioms, subsequent proofs use the axioms and previous proofs.
interpretation (In an Axiomatic System)
Also called a model, is a particular way of giving meaning to the undefined terms in the system.
independent (In an Axiomatic System)
A statement that is impossible to either prove or disprove as a logical consequence of the axioms. A good way to show that a statement is independent of the axioms is to exhibit one model for the system in which the statement is true and another model in which it is false.
consistent (In an Axiomatic System)
No logical contradiction can be derived from the axioms in the axiomatic system.
incident
Used to mean that same thing as “lie on”. As in, “P lies on l” or “P is incident with l”.
interpretation (In an Axiomatic System)
Also called a model - A particular way of giving meaning to the undefined terms in that system.
collinear
Three points that lie on the same line.
finite geometry
A geometry that contains only a finite number of points.
parallel lines
The lines do not intersect.
statement
An assertion that can be classified as true or false.
propositional function
A function whose domain consists of x numbers and whose range consist of the values “True” and “False”.
conditional statement
A compound statement of the form “If……, then…..” in which the first set of dots represents a statement called the hypothesis (or antecedent) and the second set of dots represents a statement called the conclusion (or consequent).
theorem
A conditional statement that has been proved true.
Not (P then Q)
P is true while Q is false.
converse of P then Q
Q then P
contrapositive of P then Q
Not Q then not P.
biconditional statement
“if and only if” - The statement and its converse are true.
existential quantifier
Something exists.
universal quantifier
Holds for all objects in a certain class.
negation of a quantifier
Negation interchanges the two quantifiers.
unique
Often used in connection with the existential quantifier.
Justifications for proof steps
1) by hypothesis
2) by axiom
3) by previous theorem
4) by definition
5) by an earlier step in this proof
6) by one of the rules of logic
(The reasons should be written in parenthesis after the statement)
indirect proof
Also called proof by contradiction - For proofs in the form P then Q, you assume P is true and Q is false and then show that this leads to a logical contradiction. This allows you more information to work with because you assume both P and not Q.
contrapositive proof
not Q then not P
quantifiers
One of the distinctions that must be made clear is whether you are asserting that every object of a certain type satisfies a condition or whether you are simply asserting that there is one that does.
existential quantifier
Asserts that something exists
universal quantifier
Asserts that some property holds for all objects in a certain class.