// implements BitMatrix persistable sclass BitSetMatrix extends AbstractMatrix { 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); } }