<aside> 🙋 What is so called “closed form”?

</aside>

In mathematics, an expression is in closed form if it is formed with constants, variables and a finite set of basic functions connected by arithmetic operations (+, −, ×, ÷, and integer powers) and function composition. Commonly, the allowed functions are *n*th root, exponential function, logarithm, and trigonometric functions .[1] However, the set of basic functions depends on the context.

— from 《Wikipedia》