A descriptive variable is a relation between a set of beings to be described and a set of descriptive values with the property that each being is related to exactly one descriptive value.
A descriptive variable can be noted X: Ω -> M(X), where Ω and M(X) denote the set of beings to be described, and the set of possible descriptive values, respectively.
By default, a general fact will refer to a general, descriptive, and non-tautological fact, associated with a possibly multivariate variable X: Ω -> M(X). It is a statement that is true for any element of Ω. A general fact is a negative (or restrictive) statement about at least one descriptive value of M(X): there exists a non-empty subset α of M(X) such that no being of Ω takes a value in α.
Remark: if the set Ω is unknown, the statement “there exists a non-empty subset of M(X) such that no element of Ω takes a value in it” should not be called a fact but a conjecture.