# Formal power series

## Operations

### Multiplication

Multiplying two finite formal power series is the same as multiplying two polynomials. That can be done in $O(n\log n)$ time with Fast Fourier transform

### Division

Calculating the multiplicative inverse of a formal power series can be done in $O(n\log n)$. ^{1}

### Square root

Calculating the square root of a formal power series can be done in $O(n\log n)$. ^{1}