// implements BitMatrix
persistable sclass BitSetMatrix extends AbstractMatrix<Bool> {
  new BitSet bs;
  
  *(int *w, int *h) {}
  *(int *w, int *h, BitSet *bs) {}

  public Bool get(int x, int y) { ret bs.get(y*w+x); }
  public void set(int x, int y, Bool a default true) { bs.set(y*w+x, a); }
}

Began life as a copy of #1033112