Since Donald Trump won America’s presidential election investors have been excited over the prospect of lower taxes. Mr Trump has promised to cut corporation tax from 35% to 15%. The coming reforms, though, are more than just about lower rates. Republicans want to overhaul business taxes completely. This task is far from straightforward. America’s corporate-tax rate, which reaches 39.6% once state and local levies are included, is the highest in the rich world. But a series o