This author has not been identified. Look up 'H. P. Christiansen' in GoogleThis author has not been identified. Look up 'A. Lacroix' in GoogleThis author has not been identified. Look up 'K. Lundberg' in GoogleThis author has not been identified. Look up 'A. McKeeman' in GoogleThis author has not been identified. Look up 'P. D. V. van der Stok' in Google