net logo patch patch-at错误消息

Question

我想询问当前的错误消息：

  

你不能在观察者环境中使用patch-at，因为patch = at是   龟/贴片/只

globals [payoffs]

patches-own [payments]

to setup
  clear-all
  ; green: cooperate  red: defect
   ask patches [
    set pcolor green
    set payments [ ] 
   ]

ask patch-at 1 -1 [set pcolor red]

; cooperate 0  defect 1
set payoffs [[3 0] [4 1]]

   reset-ticks
   end

to go
  tick
  ask patches [
    play
  ]
  ask patches [
    update
  ]
end