sum/3

The sum of elements of the list Vars is in relation Rel to Expr. Rel is one of #=, #\=, #<, #>, #=< or #>=. For example:

?- [A,B,C] ins 0..sup, sum([A,B,C], #=, 100).
A in 0..100,
A+B+C#=100,
B in 0..100,
C in 0..100.