• In the feature on gut microbes (14 May, p 42), the figure in the first paragraph was wrong. It should have said the bowel disease necrotising enterocolitis kills up to 5 per cent of premature babies.
• The solution we published in the 7 May issue (p 30) to Enigma puzzle 1639 “Square clocks” was wrong. In fact three unambiguous solutions are possible: square 16 with clocks 2, 7, 14; square 36 with clocks 6, 10, 15; square 81 with clocks 3, 6, 13. Apologies for the confusion.
