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Let us return briefly to the Send More Money problem
(see Constraint Satisfaction Problems). Its sum/8
predicate
will expand to a scalar_product/4
constraint. An indexical
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.