- Messier 89 (Wikipedia)
Messier 89 (M89 for short, also known as NGC 4552) is an elliptical galaxy in the constellation Virgo. It was discovered by Charles Messier on March 18, 1781. M89 is a member of the Virgo Cluster of galaxies.
- Quantifier (logic) (Wikipedia)
In logic, a quantifier is an operator that specifies how many individuals in the domain of discourse satisfy an open formula. For instance, the universal quantifier ∀ in the first order formula ∀xP(x) expresses that everything in the domain satisfies the property denoted by P. On the other hand, the existential quantifier ∃ in the formula ∃xP(x) expresses that there exists something in the domain which satisfies that property. A formula where a quantifier takes widest scope is called a quantified formula. A quantified formula must contain a bound variable and a subformula specifying a property of the referent of that variable.