capacity=

Level      c

1            10

2            20

3            40

1            5

2            0

1            1000

tuple Tcapacity
{

  int Level;
  int c;  
}
{Tcapacity} capacity = ...;

int Low[1..3];

execute{
for(var P in capacity){

if (P.Level = 1){

Low[P] = P.capacity;

}
}
}

ERROR
The collection "capacity" is immutable because it is referenced by another element.  

please help