1. Monografias de Matem�tica;E. Becker,1978
2. Becker, E., Harman, J., Rosenberg, A.: Signatures of fields and extension theory. Preprint
3. Bourbaki, N.: Elements of mathematics, commutative algebra. Reading, Mass.: Addison-Wesley 1972
4. Br�cker, L.: Characterization of fans and hereditarily pythagorean fields. Math. Z.151, 149?163 (1976)
5. Brown, R.: Superpythagorean fields. J. Algebra42, 483?494 (1976)