os.loadAPI("ocs/apis/sensor")
local s = sensor.wrap("top")

while true do

  if redstone.getInput("back") == true then
    if s.getTargetDetails("anthonybreda").IsPlayer == true then
      if s.get TargetDetails("anthonybreda").Position.Y == -1 then
      term.write("OK")
      end
    end
  end
os.sleep(1)

end