$R$ is the relation on $\mathbb{N}$ given by $a \mathrel{R} b$ if $b = a + 1$. Which of these describes $R$?

Explanation

1. 01

   $a = a + 1$ never holds, and $(1, 2)$ is in $R$ without $(2, 1)$.

2. 02

   $(1, 2)$ and $(2, 3)$ are in $R$ but $(1, 3)$ is not, since $3 \ne 1 + 1$.