 Based on the correspondence between ordering semantics and premise semantics, Kratzer (1979) mentions that Burgess’s system B is sound and complete for the latter. Veltman (1985: 108–132) proved that flat conditionals interpreted by premise semantics can be characterized by the axioms of system P. Results obtained in the 1990s show that such conditionals have an additional special property that cannot, however, be expressed as an axiom of conditional  logic:[6]