patches-own[living]

to setup

  clear-all

  ask patches [

    if random-float  < 0.3[

      set pcolor white

    ]

    set living

  ]

end

to go

  ask patches[

    set living count neighbors with [pcolor = black]

  ]

  ask patches[

  ifelse pcolor = black[

      if living >  or living < [

        set pcolor white

      ]

    ]

    [

      if living = [

        set pcolor  black

      ]

    ]

  ]

end