Every forest began with a single seed, just like every great enterprise.

At twenty-one, I was a divorced single mother. At thirty, I was struggling to feed my children. At forty, I was starting over in a new country. At fifty, I was rebuilding my career. At sixty, I walked the runway at Fashion Week. Life begins at every age—if you dare to make a plan.

The concept of polynomial-time reduction is central to understanding the structure of NP-complete problems.