translation.en: Traditionally it's been by how difficult it is to calculate, but now we can reorder it by how difficult it is to understand the concepts, however hard the calculating.
translation.zh: 以前是按照计算的难度编排课程教学的顺序， 但现在我们可以重新排序， 按照概念理念的难度， 而不管计算的难度。