// Mandatory-subset constraint: certain intervals must be selected.
// S[j] is true iff interval j is mandatory.

class Mandatory {
  boolean[] Mandatory(boolean[] S, boolean[] G) {
    forbidden (j) : S[j] && !G[j] =>
      advance : if (overlaps(j, G)) { return null; }
                else { G[j] = true; };
  }

  boolean overlaps(int j, boolean[] G) {
    boolean result = false;
    int k = 0;
    while (k < G.length) {
      if (G[k] && k != j && s[k] < f[j] && s[j] < f[k]) {
        result = true;
      };
      k = k + 1;
    };
    return result;
  }
}