Bug in sum function when input contains repeated integer values

[HuaJin16]

In model m, both c1 and c2 have a utilization of 10. We expect "query m utilSum" to return true since the total utilization is 20, but the query returns false. If we modify the utilSum rule and set s = 10, "query m utilSum" returns true.

domain Mapping
{
  Component ::= new (id: Integer, utilization: Real).
  Processor ::= new (id: Integer).
  Mapping   ::= new (c: Component, p: Processor).

  // The utilization must be > 0
  invalidUtilization :- c is Component, c.utilization <= 0.

  badMapping :- p is Processor, 
    s = sum(0.0, { c.utilization |
              c is Component, Mapping(c, p) }), s > 100.

  utilSum :- s = sum(0.0, { c.utilization | c is Component }), s = 20.

  conforms no badMapping, no invalidUtilization.
}

model m of Mapping
{
  c1 is Component(0, 10).
  c2 is Component(1, 10).
  p1 is Processor(0).
  Mapping(c1, p1).
  Mapping(c2, p1).
}

partial model pm of Mapping
{
  c1 is Component(0, x).
  c2 is Component(1, y).
  p1 is Processor(0).
  Mapping(c1, p1).
  Mapping(c2, p1).
}