I only travel with one suitcase - Mulberry does an incredible one. I always check it; the TSA restrictions are so tricky.
This is a tricky domain because, unlike simple arithmetic, to solve a calculus problem - and in particular to perform integration - you have to be smart about which integration technique should be used: integration by partial fractions, integration by parts, and so on.
Most philanthropists want to be effective altruists. But the problem isn't intention: it's measurement. Unlike financial investing, which has reporting standards, audit processes, and educational requirements, social investing is notoriously tricky to evaluate.
PayPal claims it can help merchants expand into international markets; its system makes it easier to do business with customers in multiple countries, for example, by handling tricky stuff like currency conversions automatically.