1. B. Fogg, Sheet Metal Ind. 44, 95–112 (1967)
2. W.C. Emmens, in Proceedings of the 15th IDDRG Congress (1988), pp. 63–70
3. G. Monfort, J. Defourny, in Proceedings of the 17th IDDRG Congress (1990), pp. 197–205
4. A. Azushima, in Proceedings of the 6th ICTP (1996), pp. 879–882
5. A. Azushima, K. Igarashi, K. Imai, J. Jpn. Soc. Technol. Plast. 38–436, 469–474 (1995) (in Japanese)