Authors: Le Duc, Chan¹ chan.leduc@univ-tln.fr, Le Thanh, Nhan² nhan.le-thanh@unice.fr, Rousset, Marie-Christine³ marie-christine.rousset@imag.fr

Superior Title: AI Communications. 2006, Vol. 19 Issue 3, p239-273. 35p. 7 Diagrams, 1 Chart.

Subject Terms: *MATHEMATICAL logic, *ALGORITHMS, *SEMANTICS, *HOMOMORPHISMS, *APPROXIMATION theory