 Pioneering work in the field of NMLs began with the realization that in order to give a mathematically precise characterization of defeasible reasoning CL is inadequate. Such a realization was accompanied by the effort to reproduce the success of CL in the representation of mathematical, or formal, reasoning. Among the pioneers of the field in the late 1970s were J. McCarthy, D. McDermott &amp; J. Doyle, and R. Reiter (see  Ginsberg (1987)  for a collection of early papers in the field and  Gabbay et al. (1994)  for a collection of excellent survey papers). In 1980, the Artificial Intelligence Journal published an issue (vol. 13, 1980) dedicated to these new formalisms, an event that has come to be regarded as the “coming of age” of NML. 