This picture represents transactions. $T_1$ is the time of the first transaction, $T_2$ time of second, $T_x$ time of the $x$th transaction
$t$ is the observation period, $X(t)$ denotes the number of transactions in period $t$, $x$ is the number of transactions
Can someone help me understand the following relationship: $X(t) \geq x \Leftrightarrow T_x \leq t$