// return the set of attributes,
// each attribute in the set is functionally determined by X
Set ComputeXClosure(X, F) // X: a set of attributes, F: a set of FD
{
    Set XC = X; // XC: a set of attributes
                // X -> XC (trivial because XC is X)
    bool reachClosure = false;
    while (!reachClosure) {
       reachClosure = true;
       for (each (Y -> Z) in set F) {
           if Y is subset of XC, and Z is not a subset of XC {
              // X -> XC (invariant)
              // XC -> Y (trivial because Y is a sebset of XC)
              // Y -> Z (it's given because it's in set F)
              XC = XC union Z; // X -> XC, XC -> Y, Y -> Z => X -> Z
              reachClosure = false; // just added some new attribute to XC
           }
       }
   }
   return XC;
}