and a problem in the theory of relations". Nederl. Akad. Wetensch. Proc. Ser. A 54: 371–373. Hadwiger, Hugo (1945). "Überdeckung des euklidischen Raumes
conference 1991, Resolution A4, recommendation IV, part 2 states that the unit for TT is to agree with the SI second 'on the geoid'. IAU(1991) Recommendation