Given the set $ R(x,t)= \{ (a, 1), (b, 1), (c, 1), (a, 2), (b, 2) \}$. How can I express with a first-order logic sentence "if for $t$ the amount of tuples $(x, t)$ is equal to $d$, then for $t+1$ the amount of tuples $(x,t+1)$ is equal to $d$, $d+1$ or $d-1$?
For example, at $t=1$, $d=3$ so at $t=2$ $d$ should be $2, 3$ or $1$.