Function not_equals 

pub fn not_equals<Var>(
    terms: impl Into<Box<[Var]>>,
    rhs: i32,
    constraint_tag: ConstraintTag,
) -> impl NegatableConstraint
where
    Var: IntegerVariable + Clone + 'static,

Create the NegatableConstraint ∑ terms_i != rhs.

Its negation is equals.