F. Lehmann, and R. Wille. Conceptual structures: applications, implementation and theory, 954, page 32-43. Berlin--Heidelberg--New~York, Springer--Verlag, (1995)
F. Lehmann, and R. Wille. Conceptual structures: applications, implementation and theory, 954, page 32-43. Berlin--Heidelberg--New~York, Springer--Verlag, (1995)