In
mathematics, a closure property refers to the property of a
set being
closed under some operation on its elements.
Some examples:
- the natural numbers
- are closed under addition and multiplication, but not under subtraction or division
- the regular languages
- are closed under intersection, union, complementation, and pairwise concatenation (X.Y = {x.y | x in X, y in Y}), but not elementwise concatenation (2X = {x.x | x in X })
- mankind
- is closed under multiplication, but not under its converse, unless you are a creationist