Netlogo 当所有的补丁都被着色后，如何阻止海龟

当海龟们用补丁覆盖整个世界时，我希望海龟们停在最后一个补丁上，这样我就可以记录下蜱的数量

以下是我目前的代码：

globals [marked-patches angle nextangle]

to setup   ca   ask patches   [ set pcolor black ]   crt turtle_amount
[set color red
    set size 1
    setxy (random 20) (random 20)]    reset-ticks
end

to go   ask turtles [
    fd 1
    rt random trt_ang
    lt random trt_ang
    if pcolor = black [set pcolor yellow]   ]   
tick end

---

在go中，特别是在turtle命令中，可以添加：

to go   
ask turtles [
     fd 1
     rt random trt_ang
     lt random trt_ang
         if pcolor = black [
           set pcolor yellow
           if count patches with [pcolor = black] = 0 [
               stop
           ]
    ]   
]   
             tick
     end