undo_state = nil -- undo a single move, a list of {x=,y=,cell=} squares to write to

      end,
    })
  end
  if undo_state then
    local w = App.width('undo')+10
    button(ui_state, 'undo', {x=bside-w-10, y=5, w=w, h=Line_height+10,
      bg=bg, onpress1=undo_move,
      icon=function(p)
        color(0,0,0)
        g.print('undo', p.x+5, p.y+5)

  elseif chord == 'C-z' then
    undo_move()

  local u = {
    {x=player.x, y=player.y, cell=src},
    {x=player.x, y=player.y+1, cell=dest}}

    table.insert(u, {x=player.x, y=player.y+2, cell=dest2})

  undo_state = u

  local u = {
    {x=player.x, y=player.y, cell=src},
    {x=player.x, y=player.y-1, cell=dest}}

    table.insert(u, {x=player.x, y=player.y-2, cell=dest2})

  undo_state = u

  local u = {
    {x=player.x, y=player.y, cell=src},
    {x=player.x-1, y=player.y, cell=dest}}

    table.insert(u, {x=player.x-2, y=player.y, cell=dest2})

  undo_state = u

  local u = {
    {x=player.x, y=player.y, cell=src},
    {x=player.x+1, y=player.y, cell=dest}}

    table.insert(u, {x=player.x+2, y=player.y, cell=dest2})

  undo_state = u

function undo_move()
  if undo_state == nil then return end
  for _,sq in ipairs(undo_state) do
    level_state[sq.y][sq.x] = sq.cell
  end
  undo_state = nil
end

  undo_state = nil

  undo_state = nil