Landais, P., Monthioux, M., Dereppe, J.-M., & Moreaux, C. (1988). Analyses of Insoluble Residues of Altered Organic-matter By C-13 Cp Mas Nuclear Magnetic-resonance. Organic Geochemistry, 13(4-6), 1061-1065. https://doi.org/10.1016/0146-6380(88)90289-6 (Original work published 1988)