Total relation
In mathematics, a binary relation R over a set X is total if it holds for all a and b in X that a is related to b or b is related to a (or both).
In mathematical notation, this is
Total relations are sometimes said to have 'comparability'.
For example, "is less than or equal to" is a total relation over the set of real numbers, while "is less than" is not. The relation "is a subset of" is also not total.
A common total relation is the total order.