onevent prox
# if a sensor measures a value less than 300, it does not see the table
if prox.ground.delta[0]<300 or prox.ground.delta[1]<300 then 
    # stop the motors
    motor.left.target=0 
    motor.right.target=0 
    # switch on a red light on the robot to signal an emergency stop 
    call leds.top(32, 0, 0)
else
    # if we do not see the edge of the table, switch off the red light
    call leds.top(0, 0, 0)
end