 In an influential early work on the formal study of interval-based temporal ontology and reasoning in AI, Allen (1983) considered the family of all binary relations that can arise between two intervals in a linear order, subsequently called Allen relations. These 13 relations, displayed in  Table 1,  are mutually exclusive and jointly exhaustive, i.e., exactly one of them holds between any given pair of strict intervals (excluding point-intervals). Moreover, they turn out to be definable in terms of only two of them, viz. in terms of ‘meets’ and ‘met-by’ (Allen 1983).