Past exam of the year 1 of the computer science course of the University of Oxford / 2003 / Calculus, probability, linear algebra, discrete mathematics, logic and proof, and models of computation / 6 / a / v

The “same age” binary relation is a Euclidean relation, with age understood as one consistently measured value at a fixed time. If $x$ has the same age as both $y$ and $z$, the ages of $y$ and $z$ are equal. HenceThis is another instance of equality of the values of a function inducing an equivalence relation.