struct slice {
  depth at;
  tool edges;
  grid* state;
  grid const* bit;
  grid const* goal;
  gradient block, cut;
};

void make(depth, grid const* goal, grid const* bit, grid* state, slice*);
int drill(int x, int y, slice*, machine*, grid* debug);
int mill(int x, int y, slice*, machine*, grid* debug);

void debug_map(slice const&, grid*);