 TL comprises one pair of temporal operators for the past, \(P\) and \(H\), and one pair of temporal operators for the future, \(F\) and \(G\). The operators \(P\) and \(F\) are often referred to as the ‘weak’ temporal operators, while \(H\) and \(G\) are known as the ‘strong’ ones. The respective past and future operators are duals of each other, i.e., they are interdefinable by means of the following equivalences: