• Our article on the role of science in the verification of nuclear weapons failed to make it clear that North Korea left the 1968 Nuclear Non-Proliferation Treaty in 2006 and tested a bomb at that time, as well as in May this year (27 June, p 8).
• Far from suggesting that mathematics proves that black holes do not exist, Max Wallis conceives that Einstein’s 1939 solution to the radially symmetric field equations indicates an alternative description of the collapsed object at the centre of our galaxy (20 June, p 24). Our apologies for the editing error that led to his views being misrepresented.
