Special relativity theory relies on the expression, here restricted to one spatial dimension, viz., \(x^{2} - c^{2}t^{2}\). Thus any change to new coordinates \(x'\), \(t'\), has to satisfy \(x^{2} - c^{2}t^{2} = x'^{2} - c^{2}t'^{2}\). Suppose that we write \(x = ax' + bt'\) and \(t = cx' + dt'\), then the inverse relations will be \[x' = \frac{(dx' - bt')}{(ad - bc)} \quad\text{ and }\quad t' = \frac{(ax' - ct')}{(ad - bc)}.\] If however, \(x\), \(x'\), \(t\) and \(t'\) all have to be integers, then necessarily \(ad - bc = 1\). This last condition is a pure consequence of the fact that we are thinking in a discrete way, using integers.