- Statements with “for all” and “there exist” in them are called quantified statements. “For all”, written with the symbol ∀, is called the Universal Quantifier and and “There Exists” , written with the symbol ∃, is called the Existential Quantifier. A quantifier turns a predicate such as “x is greater than 7” into a statement that can be true for false. For instance, “For all x, x is greater than 7” is false as 2 is not greater than 7, but “There Exists an x such that x is greater than 7” is true as 8 is greater than 7.
- Unidentified flying object (Wikipedia)
An unidentified flying object (UFO), or unidentified anomalous phenomenon (UAP), is any perceived airborne, submerged or transmedium phenomenon that cannot be immediately identified or explained. Upon investigation, most UFOs are identified as known objects or atmospheric phenomena, while a small number remain unexplained.