Schuecker, P., Caldwell, R. R., Böhringer, H., Collins, C. A., Guzzo, L., & Weinberg, N. N. (2003). Observational constraints on general relativistic energy conditions, cosmic matter density and dark energy from X-ray clusters of galaxies and type-Ia supernovae. Astronomy & Astrophysics, 402, 53-63. doi:10.1051/0004-6361:20030197.