This new title in the World problems series demystifies these difficult problems once and for all by showing even the most math-phobic readers simple, step-by-step tips and techniques.

And after years of delay, it's time to find a path forward on a new treaty that verifiably ends the production of fissile materials for nuclear weapons — ends it once and for all.

"We do not allow staff members to date. The reason is simple: what if they break up?" said Li Zhixin, a product director at Guangzhou Jinyi Network Technology Company.