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2. Holmbom, B., Ibid. 54:289 (1977).
3. Takeda, H., W.H., Schuller, R.V. Lawrence, and D. Rosebrook, J. Org. Chem. 34:1459 (1969).
4. Ekman, R., Personal communication.
5. Zinkel, D.F., L.C. Zank, and M. F. Wesolowski, “Diterpene Resin Acids,” USDA, Forest Service, Forest Products Laboratory, Madison WI, 1971.