python 符號運算

https://pypi.org/project/eulerlib/

http://zetcode.com/python/sympy/

https://github.com/sympy/sympy/wiki/SymPy-vs.-Mathematica

https://www.southampton.ac.uk/~fangohr/teaching/python/book/html/12-symbolic-computation.html

SymPy：使用 Python 幫你導煩人的數學公式
https://blog.gtwang.org/useful-tools/sympy-python-library-for-symbolic-mathematics/

sympy简单使用-常用函数
https://blog.csdn.net/homesangsang/article/details/83795969