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2. D.G. Jones: Trans. Inst. Mining Metall., 1974, vol. 83C, pp. 1–14.
3. I.E. Grey, D.G. Jones, and A.F. Reid: Trans. Inst. Mining Metall., 1973, vol. 82C, pp. 151–52.
4. D.G. Jones: Trans. Inst. Mining Metall., 1973, vol. 82C, pp. 186–92.
5. I.E. Grey and A.F. Reid: Trans. Inst. Mining Metall., 1974, vol. 83C, pp. 39–46.