Still on the theme "nigthmares about Prolog arithmetics", can anyone reproduce this (rather incredible) behavior? $ xsb [xsb_configuration loaded] [sysinitrc loaded] [packaging loaded] XSB Version 2.6 (Duff) of June 24, 2003 [i686-pc-linux-gnu; mode: optimal; engine: slg-wam; gc: indirection; scheduling: local] | ?- [user]. [Compiling user] write_intexpr(Term) :- M is Term, write(M). [user compiled, cpu time used: 0.0300 seconds] [user loaded] yes | ?- write_intexpr(1+1). 1 + 1 yes | ?- Term = 1+1, M is Term, write(M). 2 Term = 1 + 1 M = 2 yes | ?- If this is confirmed as a bug, does anyone know if there is a workaround that is general enough? While we are at it, do you know if XSB is still actively maintained? I sent a message to xsb-development back in April and never got a reply. All the best, Roberto -- Prof. Roberto Bagnara Computer Science Group Department of Mathematics, University of Parma, Italy http://www.cs.unipr.it/~bagnara/ mailto:bagnara@cs.unipr.it