References
- Cimprič , J. 1999 . Orderings of higher level on Noetherian rings . Comm. Algebra , 27 ( 10 ) : 5083 – 5096 .
- Cimprič , J. 2000 . Complete precones on noncommutative integral domains . Comm. Algebra , 28 ( 1 ) : 103 – 119 .
- Cimprič , J. Real spectra of quantum groups. To appear in J. Algebra
- Craven , T. 1982 . Witt rings and orderings on skew fields . J. Algebra , 77 : 74 – 96 .
- Delzell , C. N. 1984 . A continuous, constructive solution to Hilbert's 17th problem . Invent. Math. , 76 : 365 – 384 .
- Guangxin , Z. 1989 . Homogeneous Stellensätze in semialgebraic geometry . Pacific J. Math. , 136 : 103 – 122 .
- Kaiser , R. 1997 . Das Sphärische Spektrum Eines Graduierten Ringes Regensburg
- Knebusch , M. and Scheiderer , C. 1989 . Einführung in die reelle Algebra Braunschweig und Wiesbaden : Friedr. Vieweg & Sohn .
- Krivine , J.-L. 1964 . Anneaux préordonnés . J. Analyse Math. , 12 : 307 – 326 .
- Kuhlmann , S. and Marshall , M. 2002 . Positivity, sums of squares and the multidimensional moment problem . Trans. AMS , 354 : 4285 – 4301 . [CROSSREF]
- Leung , K. H. , Marshall , M. and Zhang , Y. 1997 . The real spectrum of a noncommutative ring . J. Algebra , 198 : 412 – 427 . [CROSSREF]
- Marshall , M. 2000 . Positive Polynomials and Sums of Squares Pisa, , Roma : Istituti Edit. Poligraf. Int .
- Marshall , M. 2003 . Approximating positive polynomials using sums of squares . Canad. Bull. Math. , 46 : 400 – 418 .
- Marshall , M. and Zhang , Y. 1999 . Real places and valuations on noncommutative integral domains . J. Algebra , 212 : 190 – 207 . [CROSSREF]
- Powers , V. 1988 . Higher level reduced Witt rings of skew fields . Math. Z. , 198 : 545 – 554 .
- Powers , V. 1990 . Higher level orders on noncommutative rings . J. Pure Appl. Algebra , 67 : 285 – 298 . [CROSSREF]
- Powers , V. 1991 . Holomorphy rings and higher level orders on skew fields . J. Algebra , 136 : 51 – 59 . [CROSSREF]
- Powers , V. and Scheiderer , C. 2001 . The moment problem for non-compact semialgebraic sets . Adv. Geom. , 1 : 71 – 88 .
- Schmüdgen , K. 1991 . The K-moment problem for compact semi-algebraic sets . Math. Ann. , 289 : 203 – 206 .
- Stengle , G. 1974 . A Nullstellensatz and a Positivstellensatz in semialgebraic geometry . Math. Ann. , 207 : 87 – 97 .
- Stengle , G. 1979 . Integral solution of Hilbert's seventeenth problem . Math. Ann. , 246 : 33 – 39 .
- Stengle , G. and Yousef , H. 1994 . The spherical spectrum of a graded ring . Geometriae Dedicata , 52 : 195 – 208 .
- #Communicated by A. Prestel.