Pascal’s Identity

Pascal's Identity (PI)

For all positive integers $n$ and $m$ with $m<n$, we have

$\left(\genfrac{}{}{0ex}{}{n}{m}\right)=\left(\genfrac{}{}{0ex}{}{n-1}{m-1}\right)+\left(\genfrac{}{}{0ex}{}{n-1}{m}\right)$

First saw this in MATH135, seeing this again in MATH239.