• Though Pennsylvania has a history of iron mines, the iron that might be used to power fuel cells comes from coal mines’ effluent (8 December 2007, p 27).
• Increases in school enrolment and attendance worldwide reduced the number of primary-school-age children out of school by around 20 per cent between 2002 and 2006; we said wrongly that the number in school increased that much (15 December 2007, p 5).
