trichotomy

noun

1. (countable, uncountable)Division or separation into three groups or pieces.
2. (countable, uncountable)the property of an order relation whereby, given an ordered pair of elements (of a given algebraic structure), exactly one of these is true: the first element is 'less than' the second one, the second is 'less than' the first, or the two elements are equal.

   “[A linear order] obeys the following trichotomy law[.]”