Page proofs will be sent to the corresponding author for final checking. Corrections to the proofs must be restricted to printer’s errors: any other changes to the text, in equations or grammar, may be charged to the author. Proofs should be returned to the editors within three days of receipt to minimize the risk of the author’s contribution having to be held over to a later issue. The editors do not accept responsibility for the correctness of published content. It is the author’s responsibility to check the content at the proof stage.