<a href="https://doi.org/10.53656/math2021-2-11-res" target="_blank" rel="noopener noreferrer">https://doi.org/10.53656/math2021-2-11-res</a> <span style="color: #ff0000;"><a style="color: #ff0000;" href="https://azbuki.bg/wp-content/uploads/2021/04/Resheniq-ot-br.-1.pdf" target="_blank" rel="noopener noreferrer">Отвори пълния текст</a></span>
