Recent content by AlexKryuchkov

the simplest example is if you have \int \frac{f(x)}{\text{i$\epsilon $}+x} \, dx so sometimes it is usefull to rewrite it in way \int \frac{f(x)}{\text{i$\epsilon $}+x} \, dx=P \int \frac{f(x)}{x} \, dx-i \pi f(x) where P means that you integrate in terms of principal value