Zusammenfassung der Ressource
Predicate Logic and Quantifiers
- "In predicate logic, propositions depend on variables x, y, z, so their truth value may change
depending on which values these variables assume: P(x), Q(x, y), R(x, y, z)"
- QUANTIFIERS
- ∃ (existential quantifier)
- ∃xP(x) is true if P(x) is true for some value of x
- ∀ (universal quantifier)
- ∀xP(x) is true if P(x) is true for all allowable values of x
- ∃! (for one and only one)
- ∃!xP(x) is true if P(x) is true for exactly one value and false for all other values of x
- ALTERNATION OF QUANTIFIERS
- ∀x∃y∀z P(x, y, z)
- N.B.: the order CANNOT be changed as it might modify the truth value of the statement
- NEGATION OF QUANTIFIERS
- ¬(∃xP(x)) ↔ ∀x¬P(x)
- ¬(∀xP(x)) ↔ ∃x¬P(x)