Pham, T.
(2017).
 On discretisable formulas in duration calculus.
<em>VNU Journal Of Science: Mathematics - Physics, 20</em>(1).
Retrieved from <a href="https://js.vnu.edu.vn/MaP/article/view/4115" target="_new">https://js.vnu.edu.vn/MaP/article/view/4115</a>