including those on the ancestral of a relation, in his later work The Foundations of Arithmetic. Thus, if we take xRy to be the relation y = x + 1, then 0R*y is the predicate "y is a natural number." (133) says that if x, y, and z are natural numbers, then one of the following must hold: x < y, x = y, or y < x. This is the so-called "law of trichotomy".

Influence on other works