SINCE the publication of "Capital in the Twenty-First Century", Thomas Piketty has won many plaudits for his work on inequality. The book has so far sold more than 1.5m copies. Its arguments have been praised by Nobel-prize winners and politicians alike. Last year it won the Financial Times's business book of the year award, despite the newspaper's attempts to poke holes in the book's data and arguments. On March 25th Prospect magazine put Mr Piketty atop its World Thinkers list for 2015 (alongside Yanis Varoufakis, Greece's leather-jacket wearing finance minister, Naomi Klein and Russell Brand, it should be noted). But a new challenge to Mr Piketty's book has just appeared, and from an unexpected direction.
