One of the relay circuits with single button control on and off

There are some special occasions where only one button can be used to control the on and off of electrical appliances. The following circuit can be used to achieve this.
    The circuit is shown in Figure 6-7. This circuit can realize the start, run and stop of the motor in one direction.
    When starting, press the button SB and the relay KA is closed; when the button SB is pressed for the second time, the voltage on the capacitor C3
gives a reverse voltage to the thyristor V, causing it to cut off and KA is released.