Sadatov Chori Xolmurodovich, and Qudratov Javli Xolbozorovich. “THEORETICAL FUNDAMENTALS OF STUDY PEN AND GENERAL PRINCIPLES OF DRAWING”. Galaxy International Interdisciplinary Research Journal, vol. 9, no. 10, Oct. 2021, pp. 709-16, https://giirj.com/index.php/giirj/article/view/426.