Let us return briefly to the Send More Money problem (see A Constraint Satisfaction Problem). Its sum/8
predicate
will expand to a space-efficient conjunction of library
constraints. A faster but more memory consuming version is defined
simply by changing the neck symbol of sum/8
from :-
to
+:
, thus turning it into an FD predicate:
sum(S, E, N, D, M, O, R, Y) +: 1000*S + 100*E + 10*N + D + 1000*M + 100*O + 10*R + E #= 10000*M + 1000*O + 100*N + 10*E + Y.