The Rajya Sabha today fondly remembered the sacrifices made by the four sons of Guru Govind Singh during the Mughal rule in early 18th century. Making a reference in the House, Chairman M Venkaiah Naidu said the nation cannot forget the martyrdom of the brave-hearts who showed exemplary courage in laying down their lives. <br />''<br />''The matter was raised by Sukhdev Singh Dhindsa of Shiromani Akali Dal. <br />''<br />