move_crate_to(player.y+2, player.x)
    remove_crate_from(player.y+1, player.x)

    cid = remove_crate_from(player.y+1, player.x)
    move_crate_to(player.y+2, player.x, cid)

    move_crate_to(player.y-2, player.x)
    remove_crate_from(player.y-1, player.x)

    cid = remove_crate_from(player.y-1, player.x)
    move_crate_to(player.y-2, player.x, cid)

    move_crate_to(player.y, player.x-2)
    remove_crate_from(player.y, player.x-1)

    cid = remove_crate_from(player.y, player.x-1)
    move_crate_to(player.y, player.x-2, cid)

    move_crate_to(player.y, player.x+2)
    remove_crate_from(player.y, player.x+1)

    cid = remove_crate_from(player.y, player.x+1)
    move_crate_to(player.y, player.x+2, cid)

function move_crate_to(y, x)

function move_crate_to(y, x, cid)

  assert(crate_id[y][x] == false)
  crate_id[y][x] = cid

  local result = false

    assert(crate_id[y][x])
    result = crate_id[y][x]

    assert(crate_id[y][x])
    result = crate_id[y][x]

  crate_id[y][x] = false
  return result

  crate_id = load_crate_id(level_state)

level_state = nil  -- 2D array of lh*lw sprites

level_state = nil  -- 2D array of lh*lw sprite ids
crate_id = nil  -- 2D array of lh*lw crate ids

-- sprites

-- sprite ids

  crate_id = load_crate_id(level_state)

  crate_id = load_crate_id(level_state)

  crate_id = load_crate_id(level_state)

function load_crate_id(level_state)
  local next_crate_id = 1
  local result = {}
  for r,row in ipairs(level_state) do
    local dest = {}
    for c,cell in ipairs(row) do
      if cell == CELL_CRATE or cell == CELL_CRATE_ON_TARGET then
        table.insert(dest, next_crate_id)
        next_crate_id = next_crate_id+1
      else
        table.insert(dest, false)
      end
    end
    table.insert(result, dest)
  end
  return result
end

      if crate_id[r][c] then
        color(1,1,1)
        g.print(crate_id[r][c], left+(c-1)*side, top+(r-1)*side)
      end