Thomas Piketty says governments must impose heavy taxes to break up concentrations of wealth. Edward Conard says governments should cut taxes to encourage wealthy people to pursue even bigger profits.
Simon Singh spotted the equation on a Homer Simpson blackboard. Had Homer just solved one of the toughest puzzles in math? His solution, crazily, seemed "valid" – so Singh checked Homer's numbers.
Residents of two fractious regions of eastern Ukraine began voting in a controversial referendum over sovereignty from the central government in Kiev.